The evaporation of drops of pure liquids at elevated temperatures: Rates of evaporation and wet‐bulb temperatures

Abstract

A r l z and pointing into the phase of interest. The fractional rate of change of area of surface element 4xi\zBy taking the limit as ( A x , A z ) approach zero, this expression may be rewritten for any point u, w in the interfacial surface as (A2)For an incompressible fluid this expression may be rewritten with the aid of the continuity relation to obtain auX au, u,lt) ax az The rates of evaporation and the wet-bulb temperatures have been correlated for drops of pure liquids evaporating in streams of high-temperature air. The four liquids studied were acetone, benzene, n-hexane, and water. The drops were of the order of a millimeter in diameter and were suspended in a free jet of dry, vapor-free air that ranged in temperature from 27" to 340°C. Reynolds numbers ranged from 24 to 325. Corrections to the Nusselt number to account for the heat lost to the outwardly diffusing vapor ranged up to about 35%.The correlation of the phenomena characterizing the evaporation of liquid drops under conditions leading to high heat and mass fluxes would be of interest in many fields of cominercial importance, but probably the greatest utility of such a correlation woiild be in relation to spray-drying and droplet-combustion studies. The present paper presents a simplified approach to such a correlation, being concerned solely with the evaporation of isolated pure liquid drops at atmospheric pressure. DROP EVAPORATION RATESA heat balance taken on a differential shell about a spherically symmetrical model of a drop undergoing steady state evaporation leads to the differential equation (constant film properties) ma1 conductivity of the film, is constant. In the general case, however, k will be a function of both composition and temperature. In order to maintain the simple form of Equation (1) , it is therefore necessary to define an effective average thermal conductivity of the film, to be evaluated at some appropriate composition and temperature which are as yet undefined. By designating this average thermal conductivity of the film as kf, the solution of Equation (1) is (13)To-Tl exp(-a' (RJRo)) -exp(-a') Equation ( 2 ) may now be differentiated to obtain the temperature gradient at the drop surface:The expression for the heat balance at the drop surface is (4)

A novel vaporisation model for a single-component drop in high temperature air streams

“…[17] for the evaporation of spherical drops in absence of convection. Equations (12) and (23) represent the proposed new model for evaluating sensible heat and evaporation rates from a spherical drop in hot convective environment, accounting for the explicit and important dependence of the gas density on both temperature and specie concentration.…”

“…Ranz and Marshall [11], back in 1952, proposed a comprehensive study on water and benzene evaporation at quasi steady-state conditions, reporting the evaporation rate and drop temperatures at low and moderate evaporating conditions. Few years later Downing [12] measured the quasi steady-state temperature, which is usually approximated as the wet-bulb temperature, for benzene drops and the evaporation history of hexane drops in air streams at different temperatures, while Eisenklam et al [13] measured the quasi-steady evaporation rates of different liquids in convective high-temperature air environment. The transient evaporation of a decane millimeter drop at high temperature air stream conditions has been recorded by Wong and Lin in Ref.…”

Air drying of milk droplet under constant and time‐dependent conditions

“…The heat transfer coefficient h and the mass transfer coefficient h m may be calculated from Eqs. 7 and 8 or obtained from the other established correlations 4, 11…”

Comparison of vaporization models for feed droplet in fluid catalytic cracking risers

“…In this section, the previously described four models (ITC, AS, FTC, ETC) were first evaluated against widely used experimental data of four different fluids namely water (Ranz and Marshall, 1952), hexane (Downing, 1966), heptane (Nomura et al, 1996), and decane (Wong and Lin, 1992) to compare the transient increase in droplet temperature and decrease in droplet size. Also these models were used to predict vaporization times of typical FCC feed stock i.e.…”