Investigation of the evaporation in the boundary layer

THE PURPOSE. Consider a stationary diffusion problem when a pure liquid evaporates from a flat surface of evaporation into a laminar boundary layer of a forced gas flow (in the absence of deepening of the evaporation surface and wave formation on it) at the number. In the classical model of the diffusion problem of the flow of mass from a flat surface into the laminar boundary layer, only the additional slowing down effect arising in this case is taken into account. However, the resulting solution does not correspond to the general case of evaporation, since in this case the mass transfer can significantly depend on the thermal conditions of the problem, conjugate in phases; in criterion form, this circumstance is expressed by the appearance of an additional parameter [1-3]. Note that this parameter is related to the value of the derivative of the relative concentration along the transverse coordinate on the evaporation surface. In the course of the proposed solution, the temperature of the evaporation surface and, accordingly, the value of this parameter were taken constant. METHODS. When solving the problem, we used approximate numerical methods for integrating the diffusion equation (Euler's method, integro-differential equation method, and also the method of successive approximations). In this case, the retarding effect of the vapor flow from the surface of the phase transition was assumed to be relatively insignificant in our case (which corresponded to the experimental data used in [1-3]. RESULTS. The article analyzes the well-known classical solution of the diffusion equation according to the Hartnett - Eckert model and notes that the result obtained in this case does not correspond to the general case of evaporation, when the mass transfer in the gas phase also depends on the complex. Based on the solution obtained in our work, we come to the conclusion that the effect of this parameter manifests itself in an increase in the thickness of the diffusion boundary layer. In addition, this effect is also associated with the value of the longitudinal coordinate, being more noticeable at its small values. CONCLUSION. The indicated evaporation pattern can be physically explained by a relatively larger amount of evaporated substance than in the “standard” case (since values, in turn, are associated with higher values of the evaporation surface temperature). It can also be assumed that in the region of the gas flow immediately adjacent to the evaporation surface, these factors manifest themselves in a similar way in the case of turbulent flows

Some comments on the theory of the temperature of the “wet bulb”

Clarifies the provisions of the theory of the temperature of the “wet bulb” also associated with the calculation definition