Modeling of evaporation from a sessile constant shape droplet

In this study, a computational model for the evaporation from a sessile liquid droplet fed from the center to keep the diameter of the droplet constant is presented. The continuity, momentum and energy equations are solved with temperature dependent thermo-physical properties using COMSOL Multi-physics. At the surface of the droplet, convective heat and evaporative mass fluxes are assigned. Since the flow field is affected by evaporative flux, an iterative scheme is built and the computation is automated using COMSOL-MATLAB interface. Correlations are implemented to predict the convective heat transfer coefficients and evaporative flux. Three different wall temperatures are used in simulations. The results show that the flow inside the droplet is dominated by buoyancy when the effect of the thermo-capillarity is neglected. The resulting flow generates a circulation pattern emerging from the entrance to the apex, along the surface of the droplet to the bottom heated wall and back to the entrance. © 2017 ASME The American Society of Mechanical Engineers

Two-dimensional computational modeling of thin film evaporation

A considerable amount of the evaporation originates from the close vicinity the three-phase contact line in an evaporating extended meniscus due to the low thermal resistance across the ultra thin film. Evaporation taking place within the thin film region is commonly modeled using the uni-directional flow assumption of the liquid following the lubrication approximation. Although the uni-directional flow based models may yield practically reasonable results in terms of the cumulative quantities such as total evaporation rate, the underlying physics of the problem cannot be explained solely by uni-directional flow, especially when the dominant transverse liquid motion is considered near the close proximity of the contact line. The present study develops a solution methodology to enable the solution of steady, incompressible, 2-D conservation of mass and linear momentum equations for the liquid flow in an evaporating thin film. Solution methodology includes the coupling of an uni-directional solver with high precision numerics, a higher order bi-directional spectral element solver and a finite element solver. The novelty of the present study is that steady, 2-D conservation of mass and linear momentum equations are considered in the modeling of thin film evaporation without the exclusion of any terms in the conservation equations. © 2017 Elsevier Masson SA

Design Improvement Of A Compressor Bearing Using An Elastohydrodynamic Lubrication Model

Efficiency and reliability of reciprocating hermetic compressors are of increasing interest, due to stricter energy consumption regulations and customer demands. Optimization of bearing design is particularly important, since one of the main contributors to power loss materializes at the compressor bearings. After prolonged operation, there could be scoring, sometimes scuffing or seizure at the piston pin bearing, which results in a decrease in the efficiency and reliability of the compressor. In this study a model of elastohydrodynamic lubrication of reciprocating compressor wristpin bearing was developed along with the simulation of the slider-crank mechanism of motion. Slider-crank dynamics, wristpin elastohydrodynamic and boundary lubrication, and elastic deformations are simultaneously solved in the computation. Deformations are calculated using the wristpin compliance matrix derived from a finite element model of the wristpin. The methodology was used to understand the physics of lubrication of the small end bearing, particularly the necessity of using an elastic model versus a rigid one. The design parameters were altered to reach a superior design in terms of reduced boundary lubrication and projected wear