Text a: molecular mass transfer

Термины, слова driving force - движущая сила concentration gradient - градиент

концентрации component of a mixture -

элемент/составляющая смеси mechanism - механизм, аппарат, картина,

особенность, характер molecular diffusion - молекулярная

диффузия thermal diffusion - термодиффузия to arise from - возникать в to result from - в результате чего-либо pressure diffusion - бародиффузия by virtue of - благодаря forced diffusion - вынужденная диффузия/обусловленная внешними силами

interface - внутренняя поверхность, поверхность раздела

и словосочетания

интересоваться, заниматься ч.-л. to confront - сталкиваться humidification - увлажнение cutting - резание welding - сварка ablation - оплавление heat shield - тепловой экран deaeration - деаерация feed water - питательная вода steam boiler - паровой котел heat treatment - термическая обработка

waste treatment - переработка отходов

eddy current - завихрение, вихревой ток

non-equilibrium - неравновесный

mode - вид, тип, форма, характер,

режим, метод, способ to dominate - преобладать,

господствовать moisture laden air - сильно

увлажненный воздух subsequent precipitation - последующий, выпадение/об атмосферных осадках to be concerned with -

I. Прочитайте текст, найдите ответы на следующие вопросы

1. What definition of mass transfer can you give?

2. What mechanisms of mass transfer are mentioned in the text?

3. Can you explain the difference between the words "mechanism" and "mode"?

4. What examples of mass transfer does the author give?

5. Can you add any other examples?

II. Обратите внимание на перевод следующих словосочетаний:

Forced convection mass transfer Interphase mass transfer Molecular mass transfer Convective mass transfer Moisture laden air

TEXT A

1. In this chapter another driving force, concentration gradient, is introduced. This driving force causes the transport of a component of a mixture from a region of high concentration to a region of low concentration. The transport process is known as mass transfer. The mechanisms of mass transfer are varied. They can be classified into eight types: 1. Molecular (ordinary) diffusion, resulting form a concentration gradient. 2. Thermal diffusion, arising from a temperature gradient. 3. Pressure diffusion, which occurs by virtue of a pressure gradient. 4. Forced diffusion, resulting from external forces other than gravity. 5. Forced- convection mass transfer. 6. Natural-convection mass transfer. 7. Turbulent mass transfer resulting from eddy currents in a fluid. 8. Interphase mass transfer occurring by virtue of non-equilibrium at an interface.

2. These types divide naturally into two distinct modes of transport. The first four are molecular mass transfer; the last four are convective mass transfer. Although the two modes often occur simultaneously, one mode usually dominates and we can understand the mechanisms better by considering them separately.

3. Examples of mass transfer in everyday life are legion: the diffusion of sugar in a cup of coffee; vaporization of water in a tea-kettle; the movement of moisture- laden air over the ocean with its subsequent precipitation on dry land; combustion and air-conditioning process, cloud formation; clothes drying. The chemical engineer is concerned with gas absorption, separation, crystallization and extraction, the mechanical engineer confronts the mass-transfer process in humidification, drying, cutting and welding metals, ablation of heat shields in high-speed flight, deaeration of feed water in steam boilers, and the production and heat treatment of metals; and civil engineers make use of mass transfer in waste treatment.