HMT Flashcards
The driving force in heat transfer is
temperature gradient
Under the same temperature gradient across various metal plates of the same thickness, the heat conducted per unit of surface area will be largest across
copper
If a man touches two metals which were kept together at room temperature, why would one metal feel colder than the other
one has a high thermal conductivity
Cork is a good insulator because it has
porous body
The insulation ability of an insulator with the presence of moisture would ___
Decrease
Heat transfer in turbulent flow may be described by an empirical equation correlating
Nusselt, Prandtl, and Reynold’s number
When heat is transferred from hot body to cold body, in a straight line, without affecting the intervening medium, it is referred as heat transfer by ____
radiation
An ideal surface that absorbs all incident radiation, regardless of the wavelengths and direction and is also considered to be a perfect emitter is referred to as a ____
black body
Which type of body is independent of temperature and wavelength?
graybody
In thermal radiation, the absorptivity and emissivity of a black body is ___
α= 1 and ε= 1
The Fick’s Law of Diffusion gives the rate of diffusion based on ____
a. pressure driving force
b. temperature driving force
c. concentration driving force
d. all of these
concentration driving force
It provides the basis for the quantitative description of the diffusional phenomena of molecules
Kinetic Theory of Gases
The enrichment of ethyl alcohol in the vapor phase from an aqueous ethyl alcohol solution during rectification is an example of ____
equimolal counter-diffusion
It is a measure of the diffusive mobility of individual molecules in solution
diffusion coefficient
Ammonia (A) being absorbed from air (B) into water is an example of ____
steady state unicomponent diffusion
For a gas phase diffusion, unicomponent diffusion through a gas-liquid interface will likely to occur if ____
one component is soluble and the other is not
For binary unicomponent diffusion, the concentration profile of the diffusing component along the diffusion path is ____
logarithmic
Molecular diffusivity of a liquid ____ with temperature
Increases with temperature
The method of solute transfer which involves rapid movement of large chunks of fluid in turbulent motion
eddy diffusion
The flux of A in unicomponent diffusion is different from that of equimolal counter-diffusion because of
the bulk motion of the phase
It represents the total mass transferred to mass transferred by molecular diffusion.
Sherwood Number
For turbulent mass transfer in pipes, the Sherwood number depends upon the Reynolds number (Re) as
Re^0.83
A dimensionless number that represents the ratio of the molecular momentum diffusion to the molecular mass diffusivity
Schmidt number
Unit operation that involved the concentration of a solution consisting of a non-volatile solute and a moisture solvent.
Evaporation
Evaporation is also sometimes called as
water distillation
The concentration of glycerin from a water solution by the application of heat is _____
Evaporation
The main function of baffles provided in a shell and tube heat exchanger is to
Enhance turbulence
The total amount of evaporation an evaporator is capable of producing per unit of time
Capacity
Evaporator used when the feed is hot and temperature sensitive.
Forward feed
Evaporator where pumping is not required
Forward feed
Evaporator used when feed is cold, and saving a large quantity of steam and increased economy is desired.
Backward feed
Evaporator when the upsides of backward and forward feed it desired
Mixed feed
Evaporator where feed is introduced in middle effect. It moves forward to next effect and backward to 1st effect
Mixed feed
Evaporator where fresh feed is introduced in every effect
Parallel feed
In evaporation, it is a type of feeding where the fresh solution introduced in the last effect and goes to the preceding effect where its concentration is highest.
Backward feeding
For a cold viscous feed, backward feed gives __________ than forward feed.
A. A higher capacity
B. A lower capacity
C. Lower economy
D. None of these
A. A higher capacity
The suitable evaporator for concentration of foaming liquids is a __________ .
Long tube evaporator
“Boiling point of a given solution is a linear function of the boiling point of pure water at the same pressure”
Duhring’s Rule
Boiling point rise is independent of ___
operating pressure
When the pressure of the chamber is decreased, the boiling point of the solution inside the chamber will ____
decrease
A heat transfer device that is normally used to liquefy vapors is ___
condenser
The temperature driving force in an evaporator is determined as the difference between the condensing steam temperature and
boiling point of the solution
In a country where capital is scarce and energy cost is low, which is appropriate to install?
single effect evaporator
