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If air (a non-condensing gas) is present in a condensing vapor stream, it will __________ the condensation rate of vapor.
A
Increase
B
Decrease
C
Not affect
D
Increase the condensing film co-efficient as well as
Correct Answer:
Decrease
Consider the following statements (i) If a condensing liquid does not wet a surface, then drop wise condensation will not take place on it (ii) Drop wise condensation gives a higher transfer rate than film wise condensation (iii) Reynolds number of condensing liquid is based on its mass flow rate (iv) Suitable coating or vapor additive is used to promote film wise condensation Identify the correct statement
A
i and ii
B
ii, iii and iv
C
iv only
D
i, ii and iii
The fresh feed to an ammonia synthesis reactor contains nitrogen, hydrogen and 2.0 mole per cent inerts. The molar ratio of H2:N2 is 3:1. The product stream consists of pure ammonia. Since conversion in the reactor is only 15%, a recycle stream is used and in order to avoid build-up of inerts, a purge stream is withdrawn. The rate of purge stream is adjusted to keep inert concentration in the recycle stream at 8 mole per cent. For a fresh feed rate of 100 moles/hr. Note that recycle stream contains only nitrogen, hydrogen and inerts. The N2:H2 ratio of 1:3 is maintained in every process stream, and calculate the moles of nitrogen entering the reactor and in the recycle stream?
A
125 moles/hr, 100.50 moles
B
135 moles/hr, 50 moles
C
125 moles/hr, 50 moles
D
185 moles/hr, 100.50 moles
The fresh feed to an ammonia synthesis reactor contains nitrogen, hydrogen and 2.0 mole per cent inerts. The molar ratio of H2:N2 is 3:1. The product stream consists of pure ammonia. Since conversion in the reactor is only 15%, a recycle stream is used and in order to avoid build-up of inerts, a purge stream is withdrawn. The rate of purge stream is adjusted to keep inert concentration in the recycle stream at 8 mole per cent. For a fresh feed rate of 100 moles/hr. Note that recycle stream contains only nitrogen, hydrogen and inerts. The N2:H2 ratio of 1:3 is maintained in every process stream, and calculate the number of moles, moles of inerts and moles of hydrogen in the recycle stream?
A
437 moles/hr, 35 moles/hr, 301.5 moles/hr
B
237 moles/hr, 30 moles/hr, 200 moles/hr
C
567 moles/hr, 35 moles/hr, 205 moles/hr
D
347 moles/hr, 30 moles/hr, 500 moles/hr
The fresh feed to an ammonia synthesis reactor contains nitrogen, hydrogen and 2.0 mole per cent inerts. The molar ratio of H2:N2 is 3:1. The product stream consists of pure ammonia. Since conversion in the reactor is only 15%, a recycle stream is used and in order to avoid build-up of inerts, a purge stream is withdrawn. The rate of purge stream is adjusted to keep inert concentration in the recycle stream at 8 mole per cent. For a fresh feed rate of 100 moles/hr. Note that recycle stream contains only nitrogen, hydrogen and inerts. The N2:H2 ratio of 1:3 is maintained in every process stream. Calculate the moles of ammonia produced.
A
38.90 moles/hr
B
28.90 moles/hr
C
37.50 moles/hr
D
27.50 moles/hr
The ratio of existing moles of vapor per mole of vapor free gas to the moles of vapor that would be present per mole of vapor free gas, if the mixture were saturated at the existing temperature & pressure, is termed as the
A
Relative humidity
B
Relative saturation
C
Percentage saturation
D
None of these
Statement 1: Film-type condensation has a higher heat transfer co-efficient than drop-wise condensation. Statement 2: Drop-wise condensation is easier to maintain than Film-type condensation
A
True, False
B
True, True
C
False, False
D
False, True
A thermocouple junction in the form of 4 mm radius sphere is to be used to measure the temperature of a gas stream. The junction is initially at 35 degree Celsius and is placed in a gas stream which is at 300 degree Celsius. The thermocouple is removed from the hot gas stream after 10 seconds and kept in still air at 25 degree Celsius with convective coefficient 10 W/m2 K. Find out the time constant of the thermocouple. Assume the thermos-physical properties as given below h = 37.5 W/m2 K p = 7500 kg/m3 c = 400 J/kg K
A
6.67 seconds
B
106.67 seconds
C
206.67 seconds
D
306.67 seconds
In a surface condenser, the water flowing through a series of tubes at the rate of 200 kg/hr is heated from 15 degree Celsius to 75 degree Celsius. The steam condenses on the outside surface of tubes at atmospheric pressure and the overall heat transfer coefficient is estimated at 860 k J/m2 hr degree. Find the effectiveness of the heat exchanger. At the condensing pressure, stream has a saturation temperature 0f 100 degree Celsius and the latent heat of vaporization is 2160 k J/kg. Further, the steam is initially just saturated and the condensate leaves the exchanger without sub-cooling i.e. only latent heat of condensing steam is transferred to the water. Take specific heat of water as 4 k J/kg K
A
0.224
B
0.706
C
2.224
D
3.224
In a surface condenser, the water flowing through a series of tubes at the rate of 200 kg/hr is heated from 15 degree Celsius to 75 degree Celsius. The steam condenses on the outside surface of tubes at atmospheric pressure and the overall heat transfer coefficient is estimated at 860 k J/m2 hr degree. Find the number of transfer units of the heat exchanger. At the condensing pressure, stream has saturation temperature 0f 100 degree Celsius and the latent heat of vaporization is 2160 k J/kg. Further, the steam is initially just saturated and the condensate leaves the exchanger without sub-cooling i.e. only latent heat of condensing steam is transferred to water. Take specific heat of water as 4 k J/kg K
A
3.224
B
2.224
C
1.224
D
0.224
When a stream of moist air is passed over a cold and dry cooling coil such that no condensation takes place, then the air stream will get along the line of __________
A
Constant wet bulb temperature
B
Constant dew point temperature
C
Constant relative humidity
D
Constant enthalpy