, to transfer - , , , equilibrium -
rate - , , ,
to happen -
throughout -
similar -
amount -
efflux - , , dye -
simultaneously -
flux - , ,
to interfere - ,
coolant - ,
to couple -,
to obey -
equation -
1. :
1. What characterizes transfer processes?
2. What examples are given by the author to illustrate the processes of mass transfer?
TEXT
1. The transfer process is characterized by the tendency toward equilibrium, a condition of no change. Common to a transfer process are the transport of some quantity, a driving force, and the move toward equilibrium. The characteristics of the mass of material through which the changes occur affect the rate of transport, and the geometry of the material affects the direction.
2. Consider what happens when a drop of dye is placed in water. The mass- transfer process causes the dye to diffuse throughout the water, reaching a state of equilibrium, which is easily detected visually. We can detect a similar change by smell when a small amount of perfume is sprayed into a room. The concentration becomes fainter at a point near the source as the perfume diffuses throughout the room. Anyone who has picked up a hot poker has felt the effects of heat transfer. The change in efflux of hot gases from a rocket engine can be noted by the sound. One can even sense the change by taste, as when a sugar cube dissolves and diffuses in the mouth. Hence, transfer processors are part of every day experience.
3. In general, transfer processes occur simultaneously, and sometimes the individual fluxes interfere with one another. Heat and mass transfer occur simultaneously when a coolant is forced through a hot porous plate. In thermoelectric refrigeration an electric potential is used to extract heat from a storage chamber by causing a thermal potential to develop. In most cases, however, it is possible to separate the individual phenomena, recognizing that although they are coupled in fact, they obey common physical laws and can be described by common mathematical equations.
1. , . , , . , .
2. , , . , , , . , . . - , . . , , . , .
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3. , , . , . , . , , , , .
TEXT C: FLUX DENSITY
1. . "flux". "flux" "flow" .
Flux F is the transfer rate of some quantity. It may be gallons per minute, as in the case of fluid flow; Btu per hour, as in heat transfers; or, pounds mass per hour, as in the diffusion of water vapor. While the flux of a liquid such as water is obvious, the flux associated with other transfer phenomena may be elusive to the inexperienced. The particular flux depends upon the field under consideration. It is characterized by flow (flux) lines common to the field (streamlines in the case of fluid flow). Flux is a scalar quantity; flux density is a vector.
C:
F . , ; , ; , , . , , , , . . , . ; - .
, gallon - 3,785
BTU - = 0,252 (1054, 5 )
pounds mass per hour -
vapor -
elusive - ,
stream lines - , ,
UNIT III
