HAM Flashcards
Which of the following equipment is used to convert the latent heat or sensible heat of a fluid into latent heat of vaporization of another fluid?
heat exchanger
Specifications of condenser or heat exchanger tubes are reported as BWG number. Condenser tubes having same BWG number have same ___ regardless of nominal diameter.
wall thickness
An important parameter in heat exchanger analysis, this quantity is defined as the ratio of heat exchanger’s ability to transfer heat to the fluid’s minimum ability to absorb heat.
NTU
What is the prime reason of using multi-pass shell-and-tube heat exchangers?
higher heat transfer coefficient and shorter tubes are required
Which of the following correctly describes a finned-tube heat exchanger?
large heat exchange surface per tube
Staggered configuration of bank of tubes in heat exchanger internals has a ____ pitch
triangular
The hot fluid in a concentric-tubes heat exchanger enters at 65℃ and leaves at 40℃, while cold fluid enters at 15℃ and leaves at 45℃. From the information given we can deduce that
the heat exchange operates in counterflow configuration
The hot fluid in a concentric-tubes heat exchanger enters at 65℃ and leaves at 40℃, while cold fluid enters at 15℃ and leaves at 45℃. If the heat exchanger were practical, what would be its expected effectiveness?
0.50
Theoretically, what is expected of a cooling tower that is designed based on approach = 0?
The tower is impractically high
In cooling tower design and operating, the term range refers to the
difference between hot and cold water temperatures
When will the wet-bulb temperature be equal to the dry-bulb temperature for air-water vapor systems
when RH = 100%
The portion of the moisture content of a solid material that can be removed by drying using air at constant drying conditions is called
free-moisture content
A measure of evaporator performance defined as the number of kg solvent vaporized per kg steam fed to the evaporator
economy
The driving force in heat transfer occurring in evaporator is equal to the
difference between the temperature of the solution and of the steam
In a forward-feed multiple-effect evaporator units, which of the following is true
The viscosity of the liquid is highest in the first effect
The solution is transported through effects by a pump
No pump is needed to withdraw the concentrate from the last effect
Boiling point elevation is the highest in the last effect
Boiling point elevation is the highest in the last effect
Which feeding strategy in multiple-effect evaporators is most recommended to concentrate a cold viscous feed, i.e. honey?
backward feeding
What is the effect of BPR in multiple-effect evaporator system?
reduces capacity
Which of the following is most likely the effect of lowering the temperature of the feed to the evaporator?
reduced economy
Which of the following state the Duhring’s principle?
The boiling point elevation of an aqueous solution is proportional to the concentration
The solubility of anhydrous sodium sulfate in water decreases with temperature. What is the most suitable evaporator for concentrating an aqueous solution of a material like sodium sulfate?
vacuum evaporator
Which of the following is an example of liquid-film-controlled absorption
absorption of carbon dioxide in water
Which of the following air-conditioning processes occurs at constant dew point temperature
heating
The ____ of an air-water vapor system is defined as the kg of water vapor, with partial pressure equal to its vapor pressure, contained in 1 kg of dry air.
saturation humidity
For air-water vapor system at low pressures, the adiabatic saturation temperature is equal to the ____.
wet-bulb temperature
A given amount of wet air is cooled at constant dew point and constant total pressure. Which of the following is not possible to occur?
The enthalpy of air will increase
For air-water vapor system, when will dry-bulb temperature be equal to the wet-bulb temperature?
when relative humidity reaches 100%
Why are induced-draft towers generally preferred to other intermediate-sized water-cooling towers?
Induced-draft towers prevent recirculation of the humidified air
Which of the following does not occur in a water-cooling tower?
The humidity of the air decreases
Which of the following list the principles involved in water-cooling towers?
latent heat transfer, sensible heat transfer, mass transfer, humidification
The equilibrium curve required in the design of the water cooling tower is a plot of
enthalpy of the air and temperature of the water
In the drying of a wet solid material at constant drying conditions, the total drying is the sum of the drying time in the constant-rate period and drying time in the falling-rate period if
the initial free-moisture content is greater than the critical free-moisture content.
Which drying period at constant drying conditions is usually divided into two zones - the unsaturated surface drying and the internal moisture movement?
falling-rate period
In some materials, the movement of moisture during drying at constant conditions in the falling-rate period is controlled by diffusion. Of the four materials listed, identify the one which most likely will not exhibit this mechanism?
clay
sand
starch
textile
sand
If the rate of interphase mass transfer is high and the surface area for transfer is large, then the height of a transfer unit in the packed column is ___.
small
In the design of packed columns, the diameter and the pressure drop across the packed height are estimated based on the
flooding velocity of the gas
Which quantity is used as a measure of the separation effectiveness of the particular
packing material for the species being processed in the packed column?
HTU
Why is the triangular pitch preferred to square pitch tube layout in shell-and-tube heat exchangers?
It facilitates easier cleaning of external surfaces of the tubes, resulting in lower maintenance cost.
How will the LMTD correction factor or fudge factor change as the number of shell-passes is increased in a shell-and-tube heat exchanger?
increase
The simplest type of heat exchanger is the
double-pipe heat exchanger.
What is the main reason for using multi-pass heat exchangers?
To obtain higher U and shorter tubes
Which one characteristic is common to most heat exchangers?
A solid boundary separates the hot fluid and cold fluid.
What is the major disadvantage of the double-pipe heat exchanger?
low heat-transfer surface
Which type of heat exchanger do you recommend for applications which require large heat transfer surface?
Double-pipe heat exchanger
In shell-and-tube heat exchangers, baffles are usually not needed if
condensing vapor on the shell-side serves as the heating medium.
In shell-and-tube heat exchangers, where must the cleaner or less corrosive fluid be placed?
tube-side
In shell-and-tube heat exchangers, where must a highly viscous fluid be placed?
tube-side
To avoid expensive high-pressure shells in shell-and-tube heat exchangers, high-pressure fluid should flow through ___.
the tubes
In a water to air heat exchanger, it is important to place fins on the air side because
it effects good mixing of the gas and this promotes good heat transfer.
What is the primary purpose of installing baffles in shell-and-tube heat exchangers?
To increase the convection coefficient of the shell-side fluid
The deposition of film or scale on the surface of the heat exchanger causes all of the
following except:
Decreased overall heat-transfer coefficient
Increased resistance to heat transfer between fluids
Lowered exit temperature of the cold fluid
Lowered exit temperature of the hot fluid
Lowered exit temperature of the hot fluid
Oil, flowing in the inner tube, is being heated by a saturated steam, condensing at 1.30 bars in the annular space of a double-pipe heat exchanger. The overall heat-transfer coefficient for this system is expected to be
closer to the value of oil-side heat transfer coefficient.
The fouling factor, Rf, depends on which of the following: (a) operating temperature; (b) fluid velocity; and, (c) length of service?
a, b, and c
The fouling factor, Rf, depends on which of the following: (a) operating temperature; (b) fluid velocity; and, (c) length of service?
a, b, and c
Which of the following fluid combinations is expected to have the highest U?
Steam condenser (water in tubes)
Which set of factors affect the value of the fudge factor, F?
Exit temperatures, inlet temperatures, and heat exchanger type
The fudge factor, F, is a function of R and S. If either R or S is zero, then all of the following are (or may be) true except:
One fluid stream has negligible heat capacity
Which of the following defines maximum possible heat-transfer rate?
qmax = Cmin(Th,i – Tc,i)
Which of the following does not necessarily apply to boilers and condensers?
Cmin = 0
In which double-pipe heat-exchanger flow configuration is the temperature driving force decreasing toward the outlet of the heat exchanger?
Parallel flow
If the temperature change of either fluid in a shell-and-tube or cross-flow heat exchanger is negligible, then correction factor (fudge factor) for LMTD is ___.
1
If the hot fluid stream is a condensing vapor, then Cr = Cmin/Cmax =
∞
The product of mass flow rate and heat capacity is called the
heat capacity rate
Extended surfaces are normally installed at the fluid side of the heat exchanger where
the convective coefficient is low
Mean temperature difference (MTD) and LMTD have practically same numerical values for which of the following situations?
When driving force does not vary much
Which of the following is an example of a compact heat exchanger?
Tube-plate heat exchanger
The relation, NTU = -ln(1-ε), applies to all heat exchangers as long as
Cmin/Cmax = 0
In tube bundles inside shell-and-tube heat exchangers, the shortest distance between
adjacent tubes is called the ___.
tube clearance
In tube bundles inside shell-and-tube heat exchangers, the shortest center-to-center distance between adjacent tubes is called the ___.
tube pitch.
Which of the following is true as regard square pitch in tube bundles in shell-and-tube heat exchangers?
It makes the tubes more available for external cleaning
Which feeding strategy in multiple-effect evaporation is required if the final concentrated product is highly viscous?
backward feeding
Improving the economy of an evaporator system by using multiple effect evaporator system results to
decreased capacity
Which of the following evaporator types is not well suited to concentrate heat-sensitive materials?
Forced-circulation evaporator
Which of the following is true as regard evaporation as a unit
operation?
involves the principle of decreasing the solubility of solid
Each Duhring line indicates that
the BPR of a solution is proportional to the concentration of the
solution
Which feeding strategy in multiple-effect evaporation is required if the final concentrated has a tendency to decompose at high temperature?
backward feeding
Which feeding strategy in multiple-effect evaporation requires feed pump and product pump only and no pumps in between any two effects?
forward feeding
Which of the following concepts, principles or terminologies is not
related to crystallization analysis and design?
Duhring’s law
If all crystals in magma grow in a uniform supersaturation field and at the same temperature and if all crystals grow from birth at the rate governed by the supersaturation then, according to ΔL Law, which of the following are true: (1) All crystals are of the same type; (2) All crystals have the same growth rate; (3) Crystals grow at a rate which is proportional to size?
1 and 2
Which of the following methods of accomplishes reaching supersaturation by addition of a non-solvent, which decreases the solubility of the solute?
drowning
Which of the following is not assumed by the MSMPR model?
Efficient classification of crystal sizes in the withdrawal system
