EHC Flashcards
(25 cards)
Rebelen was assigned to maintain the equipment by cleaning it. She was scolded
by her boss since she could not clean the inside of the heat exchanger. But Reb said
she would’ve cleaned it if she could. What do you think is the reason behind this?
A. The boss has a high standard in cleaning.
B. The equipment might have been blocked by foreign matters.
C. Their company uses a hairpin type which offers only surface cleaning.
D. Their company uses a Multitubular heat exchanger which does not allow tube
bundles disassembly.
C. Their company uses a hairpin type which offers only surface cleaning
You were asked to select a type of heat exchanger but only a double pipe. Your boss will be happier if you could save more money. What would you recommend?
A. Finned type
B. Multitubular
C. Shell and Tube
D. Plat heat exchangers
A. Finned type
With your knowledge in heat exchanger that at minimum temperature cross, the
effectiveness of a heat exchanger is observed to be dependent, what is your
conclusion in relation to the effectiveness of double-pipe heat exchangers?
A. Larger temperature cross provides higher efficiency. Shell and Tube is generally
more efficient than double-pipe.
B. Minimal temperature cross varies inversely with efficiency, thus double-pipe is
more efficient.
C. For smaller volumes, shell and tube is still affected by fouling factor and thus
unsuited for smaller volumes making double-pipe more efficient.
D. Both A and C
D. Both A and C
In a counterflow heat exchanger, the hot stream is cooled from 120 to 30oC while
the cold stream temperature changes from 20 to 60oC. If the same exchanger were
operated with parallel flow, what would be the exit temperatures of the two
streams?
A. 51.5oC : 50.4oC
Oil at 50oF is heated in a horizontal 2-in. Schedule 40 steel pipe 60 ft long having
a surface temperature at 120oF. The oil flow rate is 150 gal/h at inlet temperature.
What will be the oil temperature as it leaves the pipe and after mixing?
77.9 degree Fahrenheit
Oil at 50oF is heated in a horizontal 2-in. Schedule 40 steel pipe 60 ft long having
a surface temperature at 120oF. The oil flow rate is 150 gal/h at inlet temperature.
What will be the oil temperature as it leaves the pipe and after mixing? What is the average heat-transfer coefficient?
D. 8.08 Btu/h·ft2·oF
In a two effect forward feed evaporator; which statement is true
A. the temperature in the steam chest is higher in the first than in the second effect.
B. the temperature in the steam chest is lower in the first than in the second effect.
C. The pressure in the second effect must be reduced below that in the first.
D. In some cases, the first effect may be at a pressure above atmospheric
B. the temperature in the steam chest is lower in the first than in the second effect.
Compute the heat required to vaporize 1 lb of water in an evaporator producing
caustic solution containing 40% NaOH by weight, at a pressure of 3.716 psia, when
feeding 20% NaOH solution to the evaporator at the boiling temperature in the
evaporator. What is the boiling point elevation? What is the boiling point of water?
150oF
Compute the heat required to vaporize 1 lb of water in an evaporator producing
caustic solution containing 40% NaOH by weight, at a pressure of 3.716 psia, when
feeding 20% NaOH solution to the evaporator at the boiling temperature in the
evaporator. What is the boiling point elevation? The boiling point elevation?
50oF
Compute the heat required to vaporize 1 lb of water in an evaporator producing
caustic solution containing 40% NaOH by weight, at a pressure of 3.716 psia, when
feeding 20% NaOH solution to the evaporator at the boiling temperature in the
evaporator. What is the boiling point elevation? What is the heat required?
1080 BTU
A solution of organic colloids is to be concentrated from 15 to 50% solid in a vertical tube evaporator. The solution has a negligible elevation in the boiling point, and the specific heat of the feed is 0.93. Saturated steam is available at 0.8 atm abs, and the coefficient is 1700 W/m2oC. Theevaporator must evaporate 25,000 kg of
water per hour. How many square meters of surface area required?
247 m2
A solution of organic colloids is to be concentrated from 15 to 50% solid in a vertical tube evaporator. The solution has a negligible elevation in the boiling point, and the specific heat of the feed is 0.93. Saturated steam is available at 0.8 atm abs, and the coefficient is 1700 W/m2oC. The evaporator must evaporate 25,000 kg of water per hour. What is the steam consumption in kilograms per hour?
28340 kg/h
Humidification involves mass transfer between a pure liquid phase and a fixed gas
which is:
A. insoluble in the liquid
B. soluble in the liquid
C. non-ideal in nature
D. at a fixed temperature
A. insoluble in the liquid
At a fixed total pressure, humidity depends only on the
A. partial pressure of vapor in the mixture
B. heat capacity of the vapor
C. density of the vapor
D. none of these
A. partial pressure of vapor in the mixture
In saturated gas, the
A. vapor is in equilibrium with the liquid at the gas temperature
B. vapor is in equilibrium with the liquid at the room temperature
C. partial pressure of vapor equals the vapor pressure of the liquid at room temperature
D. none of these
A. vapor is in equilibrium with the liquid at the gas temperature
In an air-conditioning system, 1 kg/s air at 350 K and 10 per cent humidity is mixed with 5 kg/s air at 300 K and 30 percent humidity. What is the humidity of the resultant stream?
A. enthalpy = 76 kJ/kg
B. enthalpy = 67 kJ/kg
C. enthalpy = 87 kJ/kg
D. enthalpy = 57 kJ/kg
B. enthalpy = 67kJ/kg
0.08 m3/s of air at 305 K and 60% humidity is to be cooled to 275 K. Calculate, using a psychrometric chart, the amount of heat to be removed for each 10 deg K interval of the cooling process. What total mass of moisture will be deposited?
D. 0.0012 kg/s
Which of the following psychrometric processes is followed by water vapour laden
unsaturated air, when it is passed through solid or liquid adsorbent?
A. Cooling and dehumidification.
B. Heating and dehumidification at almost constant wet bulb temperature.
C. Dehumidification with dry bulb temperature remaining constant.
D. None of these.
B. Heating and dehumidification at almost constant wet bulb temperature
A _______ temperature is the steady state temperature attained by a small amount
of liquid evaporating into a large quantity of unsaturated gas-vapor mixture.
A. Dry bulb
B. Wet bulb
C. Dew point
D. none of these
B. Wet bulb
Which of the following is not a continuous drier?
A. Drum drier
B. Spray drier
C. Tunnel drier
D. Tray drier
D. Tray drier
During constant rate period, the rate of drying decreases with the
A. Decrease in air temperature
B. Increase in air humidity
C. both (a) and (b)
D. dehumidified
C. both (a) and (b)
The term “approach” in a cooling tower refers to the difference in the temperature
of the
A. cold water leaving the tower and the wet bulb temperature of the surrounding air
B. hot water entering the lower and the wet bulb temperature of the surrounding air
C. hot water entering and the cooled water leaving the cooling tower.
D. none of these
A. cold water leaving the tower and the wet bulb temperature of the surrounding
air
Unsaturated air (with dry and wet bulb temperatures being 35 and 25oC respectively) is passed through water spray chamber maintained at 35oC. The air will be:
A. cooled
B. humidified
C. both (a) & (b)
D. dehumidified
B. humidified
The solubility of a substance A at 25oC is 25g/L and at 50oC it solubility is 75g/L. If 500 mL of a saturated solution of A is cooled from 50oC to 25oC, how many
grams of solute A will be crystallized? Assume volume of solute in the solution is
negligible.
C. 25 g
