Description : Pick out the correct statement about the condensation. (A) Filmwise condensation gives a lower heat transfer rate than the dropwise condensation (B) Suitable coating or vapour additive is used to promote film ... place on it (D) Reynolds number of condensing liquid is based on its mass flow rate
Last Answer : (B) Suitable coating or vapour additive is used to promote film wise condensation
Description : Condensing film co-efficient for steam on horizontal tubes ranges from 5000 to 15000 Kcal/hr.m2 .°C. Condensation of vapor is carried out inside the tube in a shell and tube heat ... drop through the exchanger is desired (D) Temperature of the incoming vapor is very high
Last Answer : (B) Supersaturated
Description : Controlling heat transfer film co-efficient is the one, which offers __________ resistance to heat transfer. (A) No (B) The least (C) The largest (D) Lower
Last Answer : (C) The largest
Description : A 10 cm dia steam pipe, carrying steam at 180°C, is covered with an insulation (conductivity = 0.6 W/m.°C). It losses heat to the surroundings at 30°C. Assume a heat transfer co-efficient of 0 ... that of the un-insulated steam pipe (D) Less than the steam pipe with 5 cms insulation
Last Answer : (B) Less than that of the un-insulated steam pipe
Description : Pick out the wrong statement. (A) The condensing film co-efficient is about 3 times lower for vertical condenser as compared to the equivalent horizontal condenser for identical situation ( ... in a heat exchanger is controlled by the value of the film co-efficient, which is higher
Last Answer : (D) Overall heat transfer co-efficient in a heat exchanger is controlled by the value of the film co-efficient, which is higher
Description : Dropwise condensation occurs on __________ surfaces. (A) Clean and dirt free (B) Smooth clean (C) Contaminated cooling (D) Polished
Last Answer : (C) Contaminated cooling
Description : The most conducive surface for dropwise condensation to occur is the __________ surface. (A) Coated (B) Oily (C) Glazed & polished (D) Smooth
Last Answer : (B) Oily
Description : Dropwise condensation is promoted on a/an __________ surface. (A) Glazed (B) Oily (C) Coated (D) Smooth
Description : 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
Last Answer : (B) Decrease
Description : Pick out the wrong statement. (A) 'Solvates' are chemical compounds formed by solute with their solvents. When water is the solvent, then it is called a 'hydrate' (B) In heat exchanger ... vertical evaporators, area of central downtake is about 50 to 100% of the total tube cross-sectional area
Last Answer : (C) Heat transfer co-efficient during nucleate boiling is not influenced by the agitation imparted
Description : Even though heat transfer co-efficient in boiling liquids is large, use of fins is advantageous, when the entire surface is exposed to __________ boiling. (A) Film (B) Nucleate (C) Transition (D) All modes of
Last Answer : Option A
Description : For condensation of pure vapors, if the heat transfer co-efficients in filmwise and drop-wise condensation are respectively hf and hd , then (A) hf = hd (B) hf > hd (C) hf < hd (D) hf could be greater or smaller than hd
Last Answer : (C) hf < hd
Description : Presence of a non-condensing gas in a condensing vapour (A) Increases the rate of condensation (B) Decreases thermal resistance (C) Is desirable to increase the film co-efficient (D) None of these
Last Answer : (D) None of these
Description : If h1 = inner film co-efficient and /h2 = outer film co-efficient, then the overall heat transfer co-efficient is (A) Always less than h1 (B) Always between h1 and h2 (C) Always higher than h2 (D) Dependent on metal resistance
Last Answer : (B) Always between h1 and h2
Description : Pick out the wrong statement. (A) Superheated steam is preferably not used for process heating because of its low heat transfer film co-efficient (B) In a shell and tube heat exchanger ... surface heat exchangers, when the direction of fluid flow is parallel to the axis of the tube
Last Answer : (C) S.I. unit of fouling factor is Watt/m2 .°K
Description : Mass transfer co-efficient is directly proportional to DAB 0.5 , according to __________ theory. (A) Penetration (B) Surface renewal (C) Film (D) None of these
Last Answer : (A) Penetration
Description : Mass transfer co-efficient is directly proportional to DAB according to the __________ theory. (A) Film (B) Penetration (C) Surface-renewal (D) None of these
Last Answer : (A) Film
Description : Calculation of mass transfer co-efficient is mostly/normally done using __________ theory. (A) Surface renewal (B) Film (C) Penetration (D) None of these
Last Answer : (B) Film
Description : . A dilute aqueous solution is to be concentrated in an evaporator system. High pressure steam is available. Multiple effect evaporator system is employed, because (A) Total heat transfer area of ... in a single effect is much lower than that in any effect in a multi-effect system
Last Answer : (B) Total amount of vapor produced per Kg of feed steam in a multiple effect system is much higher than in a single effect
Description : The advantage of using a 1 - 2 shell and tube heat exchanger over a 1 - 1 shell and tube heat exchanger is (A) Lower tube side pressure drop (B) Lower shell side pressure drop (C) Higher tube side heat transfer co-efficient (D) Higher shell side heat transfer co-efficient
Last Answer : (C) Higher tube side heat transfer co-efficient
Description : Indirect contact heat exchangers are preferred over direct contact heat exchangers, because (A) Heat transfer co-efficient are high (B) There is no risk of contamination (C) There is no mist formation (D) Cost of equipment is lower
Last Answer : (B) There is no risk of contamination
Description : For a laminar flow of fluid in a circular tube, 'h1 ' is the convective heat transfer co-efficient at velocity 'V1 '. If the velocity is reduced by half and assuming the fluid properties are constant, the new convective heat transfer co-efficient is (A) 1.26 h1 (B) 0.794 h1 (C) 0.574 h1 (D) 1.741 h1
Last Answer : (B) 0.794 h1
Description : The Reynolds number of the liquid was increased 100 fold for a laminar falling film used for gas-liquid contacting. Assuming penetrating theory is applicable, the fold increase in the mass transfer co-efficient (Kc ) for the same system is. (A) 100 (B) 10 (C) 5 (D) 1
Last Answer : (B) 10
Description : Convective heat transfer co-efficient in case of fluid flowing in tubes is not affected by the tube length/diameter ratio, if the flow is in the __________ zone. (A) Laminar (B) Transition (C) Both 'a' & 'b' (D) Highly turbulent
Last Answer : (D) Highly turbulent
Description : Steam side heat transfer co-efficient in an evaporator is in the range of __________ kcal/hr.m2°C. (A) 10-50 (B) 100-500 (C) 1000-1500 (D) 5000-15000
Last Answer : (D) 5000-15000
Description : The inside heat transfer co-efficient in case of turbulent flow of liquid in the tube side in a 1-2 shell and tube heat exchanger is increased by __________ times, when the number of tube passes is increased to 8. (A) 2 0.8 (B) 4 0.8 (C) 4 0.4 (D) 2 0.4
Last Answer : (B) 4 0.8
Description : A thin, flat & square plate measuring 2 m 2 m is freely hanging in ambient air at 25°C. It is exposed to the solar radiation falling on one side of the plate at the rate of 500 W/m2. The plate temperature will ... heat transfer co-efficient is __________ W/m2 °C. (A) 50 (B) 100 (C) 150 (D) 200
Last Answer : (B) 100
Description : Mass transfer co-efficient (K) and diffusivity (D) are related according to film theory as (A) K ∝ D (B) K ∝√D (C) K ∝ D1.5 (D) K ∝ D
Last Answer : (A) K ∝ D
Description : The overall mass transfer co-efficient for the absorption of SO2 in air with dilute NaOH solution can be increased substantially by (A) Increasing the gas film co-efficient (B) Increasing the liquid film co-efficient (C) Increasing the total pressure (D) Decreasing the total pressure
Last Answer : (A) Increasing the gas film co-efficient
Description : . In a shell and tube heat exchanger, the tube side heat transfer coefficient just at the entrance of the tube is (A) Infinity (B) Zero (C) Same as average heat transfer co-efficient for tube side (D) None of these
Last Answer : (A) Infinity
Description : Steam is to be condensed in a shell and tube heat exchanger, 5 m long with a shell diameter of 1 m. Cooling water is to be used for removing the heat. Heat transfer co-efficient ... ) Horizontal heat exchanger with steam on tube side (D) Horizontal heat exchanger with steam on shell side
Last Answer : (B) Vertical heat exchanger with steam on shell side
Description : Overall heat transfer co-efficient of a particular tube is U1 . If the same tube with some dirt deposited on either side has coefficient U2 , then (A) U1 = U2 (B) U2 > U1 (C) U1 > U2 (D) U1 = dirt factor - U2
Last Answer : (A) U1 = U2
Description : In case of a vertical tube evaporator, with increase in the liquor level, the __________ is increased. (A) Velocity of circulation (B) Liquor-film co-efficient (C) Both (A) and (B) (D) Neither (A) and (B)
Last Answer : (D) Neither (A) and (B)
Description : An ideal coolant for a nuclear reactor should (A) Be a good absorber of neutrons (B) Be capable of attaining high temperature, only when it is pressurised (C) Have high density, but low heat transfer co-efficient (D) Be free from radiation damage and non-corrosive
Last Answer : (D) Be free from radiation damage and non-corrosive
Description : Double pipe heat exchangers are preferably useful, when (A) High viscosity liquid is to be cooled (B) Requirement of heat transfer area is low (C) Overall heat transfer co-efficient is very high (D) A corrosive liquid is to be heated
Last Answer : (B) Requirement of heat transfer area is low
Description : Heat transfer by natural convection is enhanced in system with (A) High viscosity (B) High co-efficient of thermal expansio
Last Answer : (B) High co-efficient of thermal expansion
Description : Baffles are provided in heat exchangers to increase the (A) Fouling factor (B) Heat transfer area (C) Heat transfer co-efficient (D) Heat transfer rate
Last Answer : (C) Heat transfer co-efficient
Description : As the difference between the wall temperature and bulk temperature increases, the boiling heat transfer co-efficient (A) Continues to increase (B) Continues to decrease (C) Goes through a minimum (D) Goes through a maximum
Last Answer : (C) Goes through a minimum
Description : The unit of heat transfer co-efficient in SI unit is (A) J/M2°K (B) W/m2°K (C) W/m°K (D) J/m°K
Last Answer : (B) W/m2°K
Description : Log mean temperature difference (LMTD) cannot be used, if (A) Heat transfer co-efficient over the entire heat exchanger is not constant (B) There exists an unsteady state (C) The heat capacity is not constant and there is a phase change (D) None of these
Description : Baffles in the shell side of a shell and tube heat exchanger (A) Increase the cross-section of the shell side liquid (B) Force the liquid to flow parallel to the bank (C) Increase the shell side heat transfer co-efficient (D) Decrease the shell side heat transfer co-efficient
Last Answer : (C) Increase the shell side heat transfer co-efficient
Description : For turbulent flow in a tube, the heat transfer co-efficient is obtained from the Dittus-Boelter correlation. If the tube diameter is halved and the flow rate is doubled, then the heat transfer co-efficient will change by a factor of (A) 1 (B) 1.74 (C) 6.1 (D) 37
Last Answer : (C) 6.1
Description : Overall heat transfer co-efficient for cooling of hydrocarbons by water is about (A) 50 -100 Kcal/hr.m2 .°C (B) 50 -100 W/m2 .°K (C) 50 -100 BTU/hr. ft. 2°F (D) 1000 - 1500 BTU/hr. ft. 2°F
Last Answer : (C) 50 -100 BTU/hr. ft. 2°F
Description : In case of vertical tube evaporator, with increase in liquor level, the overall heat transfer co-efficient (A) Increases (B) Decreases (C) Is not affected (D) May increase or decrease; depends on the feed
Last Answer : (B) Decreases
Description : Heat transfer co-efficient (h) for a fluid flowing inside a clean pipe is given by h = 0.023 (K/D) (DVρ/µ) 0.8 (CP .µ/k) 0.4 . This is valid for the value of NRe equal to (A) < 2100 (B) 2100-4000 (C) > 4000 (D) > 10000
Last Answer : (D) > 10000
Description : 1000 Kg of liquid at 30°C in a well stirred vessel has to be heated to 120°C, using immersed coils carrying condensing steam at 150°C. The area of the steam coils is 1.2 m2 and the overall heat transfer co-efficient to the ... will be (A) 15 min (B) 22 min (C) 44 min (D) 51 min
Last Answer : (D) 51 min
Description : Heat transfer co-efficient (h1 ) for liquids increases with (A) Increasing temperature (B) Decreasing temperature (C) Decreasing Reynolds number (D) None of these
Last Answer : (A) Increasing temperature
Description : Heat exchangers operating, when the asymptotic range is reached, (A) Provide very large heat transfer co-efficient (B) Results in making part of the heating surface inactive (C) Results in abruptly increased velocity (D) None of these
Last Answer : (B) Results in making part of the heating surface inactive
Description : The unit of heat transfer co-efficient is (A) BTU/hr. ft 2°F (B) BTU/hr. °F. ft (C) BTU/hr. °F (D) BTU/hr. ft
Last Answer : (A) BTU/hr. ft 2°F
Description : Heat transfer rate per unit area is called (A) Thermal conductivity (B) Heat flux (C) Heat transfer co-efficient (D) Thermal diffusivity
Last Answer : (B) Heat flux