Academic literature on the topic 'Boiling point elevation'

An analysis of the colligative properties of the elevation of the boiling point and depression of the freezing point. A unique feature of this chapter is the analysis of the depression of the freezing point, which is subtly – but importantly – different from, and much more logical than, the analysis presented in many other texts.

Colligative properties of solutions are those that depend only on the number of solute particles (molecules or ions) in the solution rather than on their chemical or physical properties. The colligative properties that can be measured experimentally include: • Vapor pressure depression • Boiling point elevation • Freezing point depression • Osmotic pressure Noncolligative properties, on the other hand, depend on the identity of the dissolved species and the solvent. Examples include solubility, surface tension, and viscosity. The addition of a solute to a solvent typically causes the vapor pressure of the solvent (above the resulting solution) to be lower than the vapor pressure above the pure solvent. As the concentration of the solute in the solution changes, so does the vapor pressure of the solvent above a solution. The vapor pressure of a solution of a nonvolatile solute is always lower than that of the pure solvent. For example, an aqueous solution of NaCl has a lower vapor pressure than pure water at the same temperature. The addition of solute to a pure solvent depresses the vapor pressure of the solvent. This observation, first made by Raoult, is now commonly known as Raoult’s law. The law states that the lowering of vapor pressure of a solution containing non-volatile solute is proportional to the mole fraction of the solute.

Evaporation is a process that involves the removal by vaporization of part of the solvent from a solution, with the objective being to concentrate the solution. In the evaporation of solutions containing biological compounds, the volatile solvent can be water or an organic solvent. Organic solvents are frequently used for antibiotics, steroids, and peptides. Often the solution is under a moderate vacuum, at pressures down to about 0.05 atm absolute [1], which is especially important for heat-sensitive biologicals where the temperature should be as low as possible to minimize degradation. The energy source for evaporation is usually steam at a low pressure, below 3 atm absolute [1]. Evaporation processes typically occur after the processes used for the removal of insolubles. They are often used to concentrate a solution just prior to the bioproduct being crystallized or precipitated. Evaporation can often be coupled with extraction: for example, a bioproduct is extracted from an aqueous stream with an organic solvent, and the extract is sent to an evaporator for concentration. In this chapter, the basic principles of evaporation are discussed, followed by a description of the most common types of evaporators for heat sensitive biological products and a discussion of scale-up and design methods. After completing this chapter, the reader should be able to do the following: • Explain the different types of resistances to heat transfer in an evaporator. • Take into account the boiling point elevation in heat transfer calculations for evaporators. • Calculate the heat transfer resistances and residence time for the concentration of a heat-sensitive bioproduct in a falling film evaporator. • Estimate the fouling factor in an evaporator. • Calculate the maximum allowable vapor velocity from an evaporator. • Select an appropriate type of evaporator to use based on the specific operational and product characteristics. • Size evaporators based on specific operating conditions and the expected overall heat transfer coefficient. The main principles to consider for evaporators are heat transfer and vapor-liquid separation. The theoretical basis of these principles will be discussed.

Dryout occurring in a heat pipe evaporator section is caused by insufficient coolant supply of wick structure, and generally considered as a failure mode of heat pipe operation. However, traditional dryout theory does not fit the bi-porous (bi-wick) wick structure research on the new mass transfer mechanism, such as liquid splash at high heat flux. The reported maximum heat flux on the similar wick structure may show a large deviation. Accordingly, dryout studies of bi-wick structures become critical and necessary to understand the limitation of the heat and mass transfer. In this article, car