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HMT Flashcards

1
Q

The driving force in heat transfer is

A

temperature gradient

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2
Q

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

A

copper

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3
Q

If a man touches two metals which were kept together at room temperature, why would one metal feel colder than the other

A

one has a high thermal conductivity

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4
Q

Cork is a good insulator because it has

A

porous body

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5
Q

The insulation ability of an insulator with the presence of moisture would ___

A

Decrease

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6
Q

Heat transfer in turbulent flow may be described by an empirical equation correlating

A

Nusselt, Prandtl, and Reynold’s number

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7
Q

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 ____

A

radiation

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8
Q

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 ____

A

black body

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9
Q

Which type of body is independent of temperature and wavelength?

A

graybody

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10
Q

In thermal radiation, the absorptivity and emissivity of a black body is ___

A

α= 1 and ε= 1

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11
Q

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

A

concentration driving force

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12
Q

It provides the basis for the quantitative description of the diffusional phenomena of molecules

A

Kinetic Theory of Gases

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13
Q

The enrichment of ethyl alcohol in the vapor phase from an aqueous ethyl alcohol solution during rectification is an example of ____

A

equimolal counter-diffusion

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14
Q

It is a measure of the diffusive mobility of individual molecules in solution

A

diffusion coefficient

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15
Q

Ammonia (A) being absorbed from air (B) into water is an example of ____

A

steady state unicomponent diffusion

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16
Q

For a gas phase diffusion, unicomponent diffusion through a gas-liquid interface will likely to occur if ____

A

one component is soluble and the other is not

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17
Q

For binary unicomponent diffusion, the concentration profile of the diffusing component along the diffusion path is ____

A

logarithmic

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18
Q

Molecular diffusivity of a liquid ____ with temperature

A

Increases with temperature

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19
Q

The method of solute transfer which involves rapid movement of large chunks of fluid in turbulent motion

A

eddy diffusion

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20
Q

The flux of A in unicomponent diffusion is different from that of equimolal counter-diffusion because of

A

the bulk motion of the phase

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21
Q

It represents the total mass transferred to mass transferred by molecular diffusion.

A

Sherwood Number

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22
Q

For turbulent mass transfer in pipes, the Sherwood number depends upon the Reynolds number (Re) as

A

Re^0.83

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23
Q

A dimensionless number that represents the ratio of the molecular momentum diffusion to the molecular mass diffusivity

A

Schmidt number

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24
Q

Unit operation that involved the concentration of a solution consisting of a non-volatile solute and a moisture solvent.

A

Evaporation

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25
Evaporation is also sometimes called as
water distillation
26
The concentration of glycerin from a water solution by the application of heat is _____
Evaporation
27
The main function of baffles provided in a shell and tube heat exchanger is to
Enhance turbulence
28
The total amount of evaporation an evaporator is capable of producing per unit of time
Capacity
29
Evaporator used when the feed is hot and temperature sensitive.
Forward feed
30
Evaporator where pumping is not required
Forward feed
31
Evaporator used when feed is cold, and saving a large quantity of steam and increased economy is desired.
Backward feed
32
Evaporator when the upsides of backward and forward feed it desired
Mixed feed
33
Evaporator where feed is introduced in middle effect. It moves forward to next effect and backward to 1st effect
Mixed feed
34
Evaporator where fresh feed is introduced in every effect
Parallel feed
35
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
36
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
37
The suitable evaporator for concentration of foaming liquids is a __________ .
Long tube evaporator
38
"Boiling point of a given solution is a linear function of the boiling point of pure water at the same pressure"
Duhring's Rule
39
Boiling point rise is independent of ___
operating pressure
40
When the pressure of the chamber is decreased, the boiling point of the solution inside the chamber will ____
decrease
41
A heat transfer device that is normally used to liquefy vapors is ___
condenser
42
The temperature driving force in an evaporator is determined as the difference between the condensing steam temperature and
boiling point of the solution
43
In a country where capital is scarce and energy cost is low, which is appropriate to install?
single effect evaporator
44
Compare capital cost and energy cost of single effect and multiple effect evaporators
Single effect: low capital, high energy (no vapor recycling) Multiple effect: high capital (marami haha), low energy
45
The fresh feed enters at the coldest effect.
feed-backward
46
In commercial practice, the areas in all effects for a multiple effect evaporator are ____
Constant
47
A multiple effect evaporator ______the steam cost
decreases
48
___ of the vapor is recovered and reuse in the multiple effect evaporator.
latent heat
49
It is the deposition and growth on body walls, and specially on heating surfaces, of a material undergoing an irreversible chemical reaction in the evaporator.
scaling
50
It is the formation of deposits other than salt or scale and maybe due to corrosion.
Fouling
51
The unit operation for separating a particular gaseous component from a mixture of gases due to difference in solubility of the gases in a liquid phase
Absorption
52
In a gas absorption tower, mass transfer occurs primarily from ___ to ____
Vapor phase to Liquid phase
53
Separation of a mixture of two gases by absorption in the liquid solvent depends upon the difference in their ___
solubility
54
In gas absorption, one solute is being absorbed while the rest of the components are assumed to be ______ and the liquid is ________.
components are inert liquid is non-volatile
55
Poor performance in large packed towers is due mainly to ____
Channeling (falling liquid will follow channels where some portion of the pack is dry, less contact with the liquid)
56
Ideal Operating Pressure and Temperature: Gas Absorption
Low T, High P (V->L: Desires high gas solubility)
57
In general, operating pressure should be ___ and temperature ___for an absorber, to minimize stage requirements and/or absorbent flow rate to lower the equipment volume required to accommodate the gas flow.
high P, low T
58
Ideal Operating Pressure and Temperature: Stripping / Desorption
High T, Low P (L->V: Desired low gas solubility)
59
What could be the effect of lowering the temperature of stripping?
Increased number of stages
60
The reverse is true for stripping. However, the operating pressure should not be too high and the operating temperature should not be too low as to ___ the feed gas.
condense the feed gas
61
Flooding results in ___
low tray efficiency
62
Operating velocity in a packed tower is usually ___
half the flooding velocity
63
Flooding in a column results due to ____
64
Channeling in a packed tower results from ____
low tray efficiency
65
Process whereby a solution becomes supersaturated so as to cause the formation of crystals
Crystallization
66
In industrial crystallization from a solution, the two phase mixture of mother liquor and crystals of all sizes, which occupies the crystallizer and is withdrawn as product is called ___
magma
67
In practice, slow cooling maintaining a low level of supersaturation produces ___ crystals and fast cooling produces ___ crystals.
large, small
68
It is the process by which crystalline bodies are created within a supersaturated fluid.
nucleation
69
When a solution is cooled to produce a supersaturated solution and hence to cause crystallization, the heat that must be removed is the sum of the ____ necessary to cool the solution and the heat of crystallization.
sensible heat content
70
Crystallization Equipment: 1. by Heating 2. by Cooling 3. by Vacuum 4. by Seeding
1. by Heating Oslo Crystallizer 2. by Cooling Swenson-Walker, Pan Coolers, Agitated Batch Coolers 3. by Vacuum Vacuum Crystallizers 4. by Seeding Mixed-Suspension Mixed-Product Removal (MSMPR)
71
Which of the following processes may always be regarded as a constant-humidity process? a. cooling of air b. air conditioning c. water-cooling in a cooling tower d. heating of air
heating of air (no condensation)
72
Wet bulb and dry bulb temperatures become identical at _____
100% RH (full saturation)
73
Steady state temperature reached by a small amount of liquid evaporating into a large amount of unsaturated vapor-gas mixture is _____
Wet-bulb temperature
74
Explain wet bulb temperature
Steady state temperature reached by a small amount of liquid evaporating into a large amount of air
75
The degrees of freedom associated with a humidification process is __
2 See Psychrometric Charts
76
What happens at dew point?
Air gets saturated with water (100% RH%). Water condenses.
77
Which of the following remains constant during sensible cooling process?
specific humidity & partial pressure of vapor
78
During sensible cooling process, ____
relative humidity & wet bulb temperature increases
79
Transfer of liquid from a wet solid into an unsaturated gas phase
Drying
80
For drying, the moisture content at end of constant rate period and beginning of fall rate period is ___
Critical moisture, Xc
81
To remove all the moisture from a wet solid requires exposure to ____ a. perfectly dry air b. air at high temperature c. highly humid air d. none of these
Perfectly dry air
82
Moisture contained by a substance in excess of the equilibrium moisture is called the __________ .
Free moisture
83
Moisture in a substance exerting an equilibrium vapour pressure less than that of pure liquid at the same temperature is called the __________ .
Bound moisture
84
Moisture content of a substance when at equilibrium with a given partial pressure of the vapour is called the __________ .
Equilibrium moisture
85
Moisture in a solid exerting an equilibrium vapour pressure equal to that of the pure liquid at the same temperature is called the __________ .
Unbound moisture
86
Why, in actuality, we cannot perfectly dry materials?
Because air has moisture content. Perfectly dry air need to perfectly dry materials.
87
When a wet solid is brought in contact with air, the solid tends to lose moisture if the air is ___
has lower humidity than the humidity corresponding to the moisture content of the solid
88
The portion of water in the wet solid that cannot be removed by the air in its contact is called _____
equilibrium moisture content
89
Moisture contained by a substance in excess of the equilibrium moisture is called ____
Free moisture
90
When drying banana chips under the sun, the rate of drying is faster on a ___
hot and windy day
91
What happens during constant rate and falling rate drying periods?
CRP: constant rate because surface moisture is readily replenished by moisture underneath the surface FRP: surface moisture no longer replenished.
92
The critical moisture content in case of drying indicates ____
beginning of falling rate period NOT IN ANSWER: or end of constant rate period
93
In drying at the falling rate period, the rate at which moisture is removed from the solid material ____
decreases with time
94
Used to cool large amounts to liquids
Cooling tower
95
Used for drying pasty materials such as wet filter cakes and lumpy solids
tray drier
96
Used for drying pastes
Drum driers or Rotary Vacuum Dryer
97
Heat sensitive materials like certain pharmaceuticals and food stuff can be dried by ____
freeze drying or vacuum drying
98
Other term for freeze drying.
Lyophilization
99
Detergent solution is dried to a powder in a ____
Spray dryer
100
Calcium ammonium nitrate (a fertilizer) is dried in a _____
rotary dryer
101
Rotary dryer cannot handle ____
Sticky materials
102
Describe temperatures in ADIABATIC DRIER
Temperature of the solid is equal to the wet bulb temperature of air
103
The rate of evaporation at a given operating temperature in an evaporator is more when ____
the operating pressure is low
104
The mode of heat transfer that can take place in a vacuum is known as ___
Radiation
105
What do you call the effectiveness of a body as a thermal radiator at a given temperature?
emissivity
106
Viscosities can change with time assuming all other conditions to be constant. If the viscosities increases with time up to a final value how do you call the fluid?
rheopectic fluid
107
"The amount of radiation emitted in all directions and overall niblings by a perfect emitter is proportional to the fourth power of the absolute temperature of the emitter."
Stefan Boltzmann Law
108
An ideal surface that absorbs all incident radiation regardless of the wavelength and direction and is also considered as a perfect emitter is referred to as ____
black body

ChE LE Flashcards (20 decks)

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