Search

Freezing and solidification processes are discussed and modeled for liquid droplets which undergo first-order phase transitions. First, a four-stage model is presented which accounts for supercooling, nucleation, recalescence, and crystallization. Subsequently, a more detailed discussion of a three-stage solidification model for droplets that do not exhibit supercooling is given. Aspects of the three-stage model validation are presented for a single cocoa butter drop and for a cocoa butter spray. [ABSTRACT FROM AUTHOR]

Evaporation of multi-component liquid droplets is reviewed, and modeling approaches of various degrees of sophistication are discussed. First, the evaporation of a single droplet is considered from a general point of view by means of the conservation equations for mass, species and energy of the liquid and gas phases. Subsequently, additional assumptions and simplifications are discussed which lead to simpler evaporation models suitable for use in CFD spray calculations. In particular, the heat and mass transfer for forced and non-forced convection is expressed in terms of the Nusselt and Sherwood numbers. Finally, an evaporation model for sprays that is widely used in today΄s CFD codes is presented. [ABSTRACT FROM AUTHOR]

Slip-flow convection heat transfer in thermal entry region of a rectangular microchannel is investigated. The wall heat flux is peripherally constant and varies exponentially with respect to the axis of the microchannel. The flow is assumed to be hydrodynamically fully developed. The three-dimensional energy conservation equation is solved numerically for different aspect ratios. Surface interaction parameters consist of momentum accommodation coefficient and thermal accommodation coefficient, are introduced to the simulation and their effects on heat transfer is investigated. The fully-developed Nusselt numbers are obtained for different values of the parameter defined in the exponential function of heat flux. For a special case, i.e., constant wall heat flux, the results are compared with those presented in literature. It was observed that two dimensionless variables that include rarefaction and surface interactions affect Nusselt number. For a specific value of thermal dimensionless variable, there is a transition region between continuum regime and slip-flow regime. Beyond this value, Nusselt number decreases as the momentum dimensionless variable increases. [ABSTRACT FROM AUTHOR]