Evaporation and Vaporization

Solvents are classified according to their boiling point ranges into  

The boiling point of a liquid is defined as the temperature at which the vapor pressure of the liquid reaches 101.3 kPa. Thermal energy is consumed in the evaporation of a liquid and is extracted from the surroundings, resulting in cooling. 

Since these factors all depend on one another, it is impossible to give a theoretical prediction of the rate of evaporation [14.69]-[14.75], In practice, the evaporation time of a given amount of solvent is determined experimentally under identical external conditions and compared with that of diethyl ether, or in some countries with that of butyl acetate. 

The results are termed evaporation numbers (Table 9) and are referred to diethyl ether = 1. Evaporation numbers are listed in Table 23. 

Solvents can be subdivided into four groups on the basis of their evaporation numbers  

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These tanks are designed to reduce evaporation and vapor emission. Two distinct designs are those with and those without an additional fixed roof. Of the former types, known as internal floating roof tanks, various provisions... 

This is a process mainly used in power plants for separation of dissolved matters by evaporation of the water. Multistage flash distillation, multiple-effect vertical long-tube vertical evaporation, submerged tube evaporation, and vapor compression are effective process equipment. It may require pH adjustment. The process removal efficiency is about 100%. 

Evaporation and vapor pressure are both explained on a molecular level by the kinetic-molecular theory developed in Section 9.6 to account for the behavior of gases. The molecules in a liquid are in constant motion, but at a variety of speeds depending on the amount of kinetic energy they have. In considering a large sample, molecular kinetic energies follow a distribution curve like that... 

Rates of Evaporation and Vapor Pressure of Sintered Beryllium (Weight losses by evaporation during one run at increasing temperature)... 

Gupta, J.P. Evaporators and vaporizers. In Fundamentals of Heat Exchanger and Pressure Vessel Technology, Hemisphere Washington, 1986 187-211. 

Both evaporation and vapor permeation process steps are carried out in a single unit. 

A quantitative analysis of the evaporation and vapor pickup begins with a mass balance on the organic species inside the evaporation cell ... 

As mentioned above, moisture in a solid may be either unbound or bound. There are two methods of removing unbound moisture evaporation and vaporization. Evaporation occurs when the vapor pressure of the moisture on the solid surface is equal to the atmospheric pressure. This is done by raising the temperature of the moisture to the boiling point. This kind of phenomenon occurs in roller dryers. 

The parameter is the maximum current density for which complete conversion of liquid water into vapor is possible. It is an important characteristic for evaluating successful CCL design. High rates of evaporation and vapor diffusion facilitate liquid-to-vapor conversion. The minimum liquid water flux relative to the total water flux at z — L is given by... 

Evaporation is energy-intensive. The latent heat associated with separation of a ton of dry NaCl from saturated solution is about 6.5 GJ. With KCl, the equivalent figure depends more on the temperature assumed for the brine as produced but is in the range of 3.5-4 GJ. Energy economization is therefore a major consideration in evaporation process design. Two different approaches are in widespread use, multiple-effect evaporation and vapor recompression. 

The primary measures of the performance of an evaporator are the capacity and the economy. Capacity is defined as the amount evaporated per hour. Economy is the ratio of the mass evaporated to the mass of heat transfer fluid (often steam) used. When evaporating water with steam, the economy is nearly always less than 1.0 for single-effect evaporators but in multiple-effect evaporators and vapor compression systems it is considerably greater. 

Increased surface area allows volatile fractions to evaporate and vapors collect in bund... 

This generalization provides the molecular explanation behind the Maxwell-Boltzmann distribution of molecular speeds (kinetic energies) that was discussed in Section 12-13 (see Figure 12-9) and in relation to evaporation and vapor pressures of liquids... 

Although both evaporation and vaporization involve the gas phase, we define a vapor pressure depression for the evaporation process, but a boiling point elevation for the vaporization process. Why must we define different phenomena if both processes involve a liquid becoming a gas ... 

In a heat pipe of constant vapor core diameter, the vapor stream accelerates and decelerates because of the vapor addition in the evaporator and vapor removal in the condenser. Velocity variations in a converging-diverging nozzle result from a constant mass flow through a variable area, whereas in a heat pipe velocity, variations result from a variable mass flow through a constant area. 

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