In a parallel flow heat exchanger, if the outlet temperature of hot and
cold fluids are the same, then the log mean temperature difference (LMTD)
is
(A) Minimum
(B) Maximum
(C) Zero
(D) Infinity
Description : Pick out the wrong statement. (A) The controlling resistance in case of heating of air by condensing steam is in the air film (B) The log mean temperature difference (LMTD) for ... a pure fluid at a given pressure from liquid to vapor or vice-versa occurs at saturation temperature
Last Answer : (C) In case of a 1 - 2 shell and tube heat exchanger, the LMTD correction factor value increases sharply, when a temperature cross occurs
Description : In a 1-1 concurrent heat exchanger, if the tube side fluid outlet temperature is equal to the shell side fluid outlet temperature, then the LMTD is (A) ∞ (B) 0 ... temperature (D) Equal to the difference between hot fluid inlet temperature and cold fluid outlet temperature
Last Answer : (B) 0
Description : LMTD for counter-flow and parallel flow heat exchanger will be the same, when the (A) Cold fluid is heated to a certain temperature by condensing steam (isothermal fluid) (B) Outlet temperature of ... temperature of hot fluid is less than the outlet temperature of the cold fluid (D) None of these
Last Answer : (A) Cold fluid is heated to a certain temperature by condensing steam (isothermal fluid)
Description : In case of parallel flow heat exchanger, the lowest temperature theoretically attainable by the hot fluid is __________ the outlet temperature of the cold fluid. (A) Equal to (B) More than (C) Less than (D) Either more or less than (depending upon the fluid)
Last Answer : (A) Equal to
Description : Parallel straight line pattern of temperature distribution for both hot and cold fluids is observed in case of heat exchanger of the type (A) Parallel flow with equal heat capacities (B) Counter ... (C) Counter flow with unequal heat capacities (D) Parallel flow with unequal heat capacities
Last Answer : (B) Counter flow with equal heat capacities
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
Last Answer : (D) None of these
Description : For a heat exchanger, will the overall heat transfer coefficient increase along with an increase in LMTD (log mean temperature difference) around the unit?
Last Answer : The overall heat transfer coefficient is generally weakly dependent on temperature. As the temperatures of the fluids change, the degree to which the overall heat transfer coefficient will be affected depends ... with temperature as I've noted and the U-value will decrease over time with fouling).
Description : In a liquid-liquid heat exchanger, for the same process temperature, the ratio of the LMTD in parallel flow to the LMTD in counter flow is always (A) < 1 (B) > 1 (C) 1 (D) ∞
Last Answer : (A) < 1
Description : The outlet temperature of cooling water in a heat exchanger is generally not allowed to exceed above 50°C in industrial practice mainly to avoid (A) Its evaporation loss (B) Excessive corrosion (C) Uneconomic LMTD (D) Decrease in heat exchanger efficiency
Last Answer : (B) Excessive corrosion
Description : LMTD for evaporators & condensers for a given terminal parameters & set of conditions for counter-flow is equal to that for parallel flow. In such heat exchangers, with one of the fluids condensing or evaporating, the surface ... Parallel (B) Mixed (C) Counter flow (D) Same in either 'a', b' or 'c'
Last Answer : (D) Same in either 'a', b' or 'c'
Description : In a heat exchanger, the rate of heat transfer from the hot fluid to the cold fluid (A) Varies directly as the area and the LMTD (B) Directly proportional to LMTD and inversely proportional to the area (C) Varies as square of the area (D) None of these
Last Answer : (A) Varies directly as the area and the LMTD
Description : Terminal point temperature differences between fluids in case of a heat exchanger is termed as (A) Approach (B) Log mean temperature difference (C) Arithmetic mean temperature difference (D) Geometric mean temperature difference
Last Answer : (A) Approach
Description : Hot water (0.01 m3 /min) enters the tube side of a counter current shell and tube heat exchanger at 80°C and leaves at 50°C. Cold oil (0.05 m3 /min) of density 800 kg/m3 and specific heat of ... mean temperature difference in °C is approximately (A) 32 (B) 37 (C) 45 (D) 50
Last Answer : (A) 32
Description : A 2-4 heat exchanger involves (A) Only counter-flow of fluids (B) Only parallel-flow of fluids (C) Both counter and parallel-flow of the fluids (D) Smaller pressure drop compared to 1-2 exchanger
Last Answer : (C) Both counter and parallel-flow of the fluids
Description : LMTD correction factor which is to be applied for a cross-flow heat exchanger increases with increase in the number of shell passes. Its value for a single pass cross flow heat exchanger is (A) 0 (B) 1 (C) > 1 (D) < 1
Last Answer : (D) < 1
Description : In a counter flow heat exchanger, hot fluid enters at 170°C & leaves at 150°C, while the cold fluid enters at 50°C & leaves at 70°C. The arithmetic mean temperature difference in this case is __________ °C. (A) 20 (B) 60 (C) 120 (D) ∞
Last Answer : (D) ∞
Description : For the same heat load and mass flow rate in the tube side of a shell and tube heat exchanger, one may use multipass on the tube side, because it (A) Decreases the pressure drop (B) ... the outlet temperature of cooling medium (C) Increases the overall heat transfer coefficient (D) None of these
Last Answer : (C) Increases the overall heat transfer coefficient
Description : For a thermodynamic process to be reversible, the temperature difference between hot body and working substance should be (a) zero (b) minimum (d) maximum (d) infinity (e) there is no such criterion.
Last Answer : Answer : a
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 : case of condensers & evaporators operating under given terminal conditions, LMTD (logarithmic mean temperature difference) for counter flow as compared to that for parallel flow is (A) More (B) Less (C) Equal (D) Much more
Last Answer : Option C
Description : It is not recommended to use a 1-2 shell and tube heat exchanger for a particular heat duty, whenever the LMTD correction factor is (A) > 0.75 (B) < 0.75 (C) < 0.50 (D) < 0.25
Last Answer : (B) < 0.75
Description : LMTD can't be used as such without a correction factor for the (A) Multipass heat exchanger (B) Baffled heat exchanger (C) Condensation of mixed vapour in a condenser (D) All (A) (B) and (C)
Last Answer : (D) All (A) (B) and (C)
Description : For a multipass shell and tube heat exchanger, the LMTD correction factor is always (A) 1 (B) > 1 (C) < 1 (D) Between 1 & 2
Last Answer : (C) < 1
Description : In counter flow compared to parallel flow, (A) LMTD is greater (B) Less surface area is required for a given heat transfer rate (C) Both (A) and (B) (D) More surface area is required for a given heat transfer rate
Last Answer : (C) Both (A) and (B)
Description : Thermal efficiency of a Carnot engine can approach 100%, only when the temperature of the (A) Cold reservoir approaches zero (B) Hot reservoir approaches infinity (C) Either (A) or (B) (D) Neither (A) nor (B)
Last Answer : C) Either (A) or (B)
Description : One item listed on the name plate of a cargo pump motor is 'degrees centigrade rise.' This number is based on _____________. A. normal temperature change from cold to hot B. an ambient temperature ... . minimum heat rise from no load to full load D. maximum degrees centigrade rise from absolute zero
Last Answer : Answer: B
Description : In a shell and tube heat exchanger, (A) The temperature drops in the two fluids and the wall are proportional to individual resistances (B) The temperature drop is inversely proportional to ... ) There is no relationship between temperature drop and resistance (D) The relationship is not generalised
Last Answer : (A) The temperature drops in the two fluids and the wall are proportional to individual resistances
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 : In a heat exchanger, floating head is provided to (A) Facilitate cleaning of the exchanger (B) Increase the heat transfer area (C) Relieve stresses caused by thermal expansion (D) Increase log mean temperature gradient
Last Answer : (C) Relieve stresses caused by thermal expansion
Description : In the equation Q = UAΔt; Δt is (A) Geometric mean temperature difference (B) Arithmetic mean temperature difference (C) Logarithmic mean temperature difference (D) The difference of average bulk temperatures of hot and cold fluids
Last Answer : (C) Logarithmic mean temperature difference
Description : Using an organic fluid that boils at a low temperature means that energy could be regeneratedfrom waste fluids is known as ________. a) Heat exchanger b) Heat remover c) Heat pumps d) Heat absorber
Last Answer : Heat pumps
Description : Extremely large or small volumes of fluids are generally best routed through the shell side of a shell and tube heat exchanger, because of the (A) Less corrosion problems (B) Flexibility possible in the baffle arrangement (C) Low pressure drop (D) High heat transfer co-efficient
Last Answer : (B) Flexibility possible in the baffle arrangement
Description : Which is the best tube arrangement (in a shell and tube heat exchanger) if the fluids are clean and non-fouling? (A) Square pitch (B) Triangular pitch (C) Diagonal square pitch chemical-engineering
Last Answer : (B) Triangular pitch
Description : Correction is applied to LMTD for __________ flow. (A) Parallel (B) Counter (C) Cross (D) None of these
Last Answer : (C) Cross
Description : If a suspended body is struck at the centre of percussion, then the pressure on die axis passing through the point of suspension will be (A) Maximum (B) Minimum (C) Zero (D) Infinity
Last Answer : (C) Zero
Description : As the temperature is lowered towards the absolute zero, the value of ∂(∆F)/∂T, then approaches (A) Unity (B) Zero (C) That of the heat of reaction (D) Infinity
Last Answer : B) Zero
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 : A process stream of dilute aqueous solution flowing at the rate of10 Kg.s -1 is to be heated. Steam condensate at 95°C is available for heating purpose, also at a rate of 10 Kg.s -1 . A 1 ... side (C) Parallel flow with process stream on shell side (D) Parallel flow with process stream on tube side
Last Answer : (A) Counter flow with process stream on shell side
Description : Recuperated will be more efficient if the flow path of hot and cold fluids is in: a) Co-current mode b) Counter current mode c) Cross current mode d) Cone of the above
Last Answer : Counter current mode
Description : Define heat exchanger. Classify heat exchangers based on geometry, direction of fluids, method of heat exchange.
Last Answer : 1. A heat exchanger is a device, which transfers thermal energy between two fluids at different temperatures. 2. In most common engineering applications, both fluids are in motion and the ... free or forced convection ii. Boiling or condensation iii. Radiation or combined convection radiation
Description : Out of the following four assumptions used in the derivation of theequation for LMTD [LMTD = (∆t1 - ∆t2 )/ln(∆t1 /∆t2 )], which one is subject to the largest deviation in practice ? (A) Constant ... (B) Constant rate of fluid flow (C) Constant specific heat (D) No partial phase change in the system
Last Answer : (B) Constant rate of fluid flow
Description : In a heat exchanger with steam outside the tubes, a liquid gets heated to 45°C, when its flow velocity in the tubes is 2 m/s. If the flow velocity is reduced to 1 m/s, other things remaining ... than 45°C (B) More than 45°C (C) Equal to 45°C (D) Initially decreases and remains constant thereafter
Last Answer : (B) More than 45°C
Description : . If a single tube pass heat exchanger is converted to two pass, then for the same flow rate, the pressure drop per unit length in tube side will (A) Increase by 1.8 times (B) Decrease by 2 2 (C) Increase by 2 16 (D) Remain unchanged
Last Answer : (C) Increase by 2 16
Description : In case of a shell and tube heat exchanger, the minimum and maximum baffle spacing is respectively (where, D = inside diameter of the shell) (A) D/5 and D (B) D/2 and 2 D (C) D/4 and 2 D (D) D and 2 D
Last Answer : (A) D/5 and D
Description : The shaft is always stepped with ________ diameter at the middle portion and __________ diameter at the shaft ends. a) Minimum, maximum b) Maximum, minimum c) Minimum, minimum d) Zero, infinity
Last Answer : b) Maximum, minimum
Description : In a co-current double pipe heat exchanger used for condensing saturated steam over the inner tube, if the entrance and exit conditions of the coolant are interchanged, then the rate of condensation ... Decrease (C) Remain unchanged (D) Either increase or decrease; depends on the coolant flow rate
Last Answer : (C) Remain unchanged
Description : To reduce the tube side pressure drop for the same flow rate, the heat exchanger recommended is (A) 1-2 heat exchanger (B) 1-1 heat exchanger (C) 3-2 heat exchanger (D) 2-4 heat exchanger
Last Answer : (B) 1-1 heat exchanger
Description : At minimum reflux ratio for a given separation (A) Number of plates is zero (B) Number of plates is infinity (C) Minimum number of the theoretical plates is required (D) Separation is most efficient
Last Answer : (B) Number of plates is infinity