Molecular simulations of droplet evaporation by heat transfer

Droplet evaporation by heat transfer is investigated by molecular dynamics simulations for a pure Lennard-Jones fluid. Two different initial conditions are treated: (1) a droplet surrounded by its vapor in equilibrium, (2) a cold droplet surrounded by warm vapor. In both cases heat is transferred from a heat bath. Results are the numbers of droplet molecules N _d and density, drift velocity, and temperature profiles as functions of time. For the small droplets considered N _d depends on the definition of a droplet molecule. The density profiles as function of time show a transition from a droplet with liquid–vapor interface to a cluster of interfacial type and finally to the gas state. The temperature at a given time is nearly constant within the droplets or clusters but strong gradients occur in the gas. In case of evaporation of a cold droplet surrounded by warm vapor we observed initially cooling down of the droplet corresponding to pressure jump evaporation and thereafter slower evaporation because of lower initial state vapor density.     

Modelling and Simulation of Momentum, Heat, and Mass Transfer in a Deep-Bed Grain Dryer

This article concerns the modelling and simulation of a deep-bed grain dryer in a large diameter-column. Two-dimensional (2D) models of deep-bed grain dryers were built by considering simultaneously momentum, heat, and mass transfer in the drying phase together with coupled heat and mass balance in the grain phase. The dynamic equations are solved numerically by using finite difference method. The momentum equations are applied to simulate pressure drop and velocity field of the drying air across the bed. The mass and heat balance in the two phases determine the profile of temperature and moisture content in both phases. Further, drying rate curves for various temperature of inlet drying gas together with moisture content of grain were simulated. The simulated profiles are in close agreement with experimental data.