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

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
by

1 Answer

Answer :

(B) 0.794 h1
by

Related questions

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

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Last Answer : (D) Highly turbulent

In case of laminar flow of fluid through a circular pipe, the (A) Shear stress over the cross-section is proportional to the distance from the surface of the pipe (B) Surface of velocity distribution is a paraboloid of revolution, whose volume equals half the volume of circumscribing cylinder (C) Velocity profile varies hyperbolically and the shear stress remains constant over the cross-section (D) Average flow occurs at a radial distance of 0.5 r from the centre of the pipe (r = pipe radius)

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Which of the following parameters is increased by use of finned tube in a multipass shell and tube heat exchanger? (A) Tube side pressure drop and the heat transfer rate (B) Convective heat transfer co-efficient (C) Effective tube surface area for convective heat transfer (D) All (A) (B) and (C)

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Last Answer : (B) 100

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What is the critical radius of insulation (cms) for a metallic cylinder, if the convective heat transfer co-efficient with the ambient atmosphere is 5 W/m2. °K? Thermal conductivity of metal and insulation material are 40 and 0.1 W/m.°K respectively. (A) 2 (B) 8 (C) 10 (D) 40

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Last Answer : (A) 2

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, the shell pressure drop is maximum for orifice baffles (C) S.I. unit of fouling factor is Watt/m2 .°K (D) Longitudinal fins are used in extended surface heat exchangers, when the direction of fluid flow is parallel to the axis of the tube

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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 deviationin practice ?(A) Constant overall heat transfer co-efficient.(B) Constant rate of fluid flow(C) Constant specific heat(D) No partial phase change in the system

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For laminar flow of Newtonian fluids through a circular pipe, for a given pressure drop and length & diameter of pipe, the velocity of fluid is proportional to (where, μ = fluid viscosity ) (A) μ (B) 1/μ (C) √μ (D) 1/√μ

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The average heat transfer co-efficient over the entire length of the plate (ha ) and the local heat transfer co-efficient (hL ), in case of heat transfer over a flat plate in laminar zone is related as (A) ha = 0.8hL (B) ha = 2hL (C) ha = hL (D) ha = 5hL

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Last Answer : (B) ha = 2hL

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Last Answer : (A) Increasing temperature

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Last Answer : (B) Always between h1 and h2

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

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Consider the following statements in respect of steady laminar flow through a circular pipe: 1. Shear stress is zero on the central axis of the pipe 2. Discharge varies directly with the viscosity of the fluid 3. Velocity is maximum at the centre of the pipe. 4. Hydraulic gradient varies as the square of the mean velocity of flow. Which of these statements are correct? (a) 1, 2 , 3 & 4 (b) 1 & 3 only (c) 2 & 4 only (d)3 & 4 only

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Last Answer : (b) 1 & 3 only

In an extended surface heat exchanger, fluid having lower co-efficient (A) Flows through the tube (B) Flows outside the tubes (C) Can flow either inside or outside the tubes (D) Should not be used as it gives very high pressure drop

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Last Answer : (B) Flows outside the tubes

Pick out the wrong statement. (A) Momentum transfer in laminar flow results from velocity gradient (B) A fluid in equilibrium is not free from shear stress (C) The viscosity of a non-Newtonian fluid is a function of temperature only (D) Both (B) and (C)

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Last Answer : (D) Both (B) and (C)

A metal wire of 0.01 m dia and thermal conductivity 200 W/m.K is exposed to a fluid stream with a convective heat transfer coefficient of 100 W/m2 .K. The Biot number is (A) 5.6 (B) 0.025 (C) 3.5 (D) 0.0035

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Last Answer : (B) 0.025

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

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Last Answer : (C) Increase the shell side heat transfer co-efficient

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

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Last Answer : (C) 6.1

The fluid velocity varies as the cube of the cylindrical pipe diameter in case of steady state laminar flow at constant pressure drop for __________ fluid. (A) Newtonian (B) Pseudo-plastic (C) Dilatent (D) Bingham plastic

Description : The fluid velocity varies as the cube of the cylindrical pipe diameter in case of steady state laminar flow at constant pressure drop for __________ fluid. (A) Newtonian (B) Pseudo-plastic (C) Dilatent (D) Bingham plastic

Last Answer : (B) Pseudo-plastic

The fluid velocity varies as the square of the cylindrical pipe diameter, in case of steady state laminar flow at constant pressure drop, for __________ fluid. (A) Newtonian (B) Dilatant (C) Pseudo-plastic (D) Non-Newtonian

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Last Answer : (A) Newtonian

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Last Answer : (A) Dilatent

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Last Answer : (B) 4.36

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Last Answer : (D) All (A), (B) and (C)

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Description : The characteristic dimensionless groups for heat transfer to a fluid flowing through a pipe in laminar flow are (A) Re.Gz (B) Nu, Pr (C) Nu, Pr, Re (D) Nu, Gz

Last Answer : (D) Nu, Gz

Maximum heat transfer rate is achieved in __________ flow. (A) Co-current (B) Counter-current (C) Turbulent (D) Laminar

Description : Maximum heat transfer rate is achieved in __________ flow. (A) Co-current (B) Counter-current (C) Turbulent (D) Laminar

Last Answer : (C) Turbulen

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For laminar flow of Newtonian fluid in a circular pipe, the velocitydistribution is a function of the distance 'd' measured from the centre line ofthe pipe, and it follows a __________ relationship.(A) Logarithmic(B) Parabolic(C) Hyperbolic(D) Linear

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Last Answer : (B) Parabolic

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Last Answer : (D) > 10000

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. In a shell and tube heat exchanger, the tube side heat transfer co￾efficient 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

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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 for the cooling water, whether on shell side or tube side is the same. The best arrangement is (A) Vertical heat exchanger with steam on tube side (B) Vertical heat exchanger with steam on shell side (C) Horizontal heat exchanger with steam on tube side (D) Horizontal heat exchanger with steam on shell side

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Last Answer : (B) Decreases

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

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Last Answer : (A) U1 = U2

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

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Last Answer : (C) Higher tube side heat transfer co-efficient

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Last Answer : (B) Flexibility possible in the baffle arrangement