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Fluid Mechanics(29)Heat Transfer(23)Thermodynamics(16)Applications (Power Engineering, I.C. Engines, Refrigeration, Turbomachinery)(8)

Fluid Mechanics

29 Questions

GATE→2026→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q1

MCQ[1 Mark]

A steady incompressible laminar flow passes through a $90^{\circ}$ tube bend placed on a horizontal surface. In horizontal diametric plane, two pressure taps $P_{i}$ and $P_{o}$ are provided across the cross-section at inner and outer walls of the bend, respectively. Which one of the following options is correct?

(A)

P_{o}>P_{i}

(B)

P_{o}<P_{i}

(C)

(P_{o}-P_{i}) is directly proportional to bend radius

(D)

(P_{i}-P_{o}) is inversely proportional to average flow velocity

Explanation

GATE→2026→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q2

MCQ[1 Mark]

An ideal gas passes isothermally through a long horizontal uniform cross-section pipe under steady flow. Consider that the pressure gradient in the pipe is sufficient for a finite change in the density of the gas. If the flow of the gas is purely pressure driven and subsonic throughout, then the average flow velocity

(A)

increases along the flow

(B)

decreases along the flow

(C)

does not change throughout the pipe

(D)

increases in the hydrodynamic entrance region and then decreases thereafter

Explanation

GATE→2026→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q3

MCQ[1 Mark]

Bernoulli's equation CANNOT be applied between

(A)

any two arbitrary points in the flow field for steady incompressible rotational flow

(B)

any two arbitrary points in the flow field for steady incompressible irrotational flow

(C)

any two points along a streamline for steady incompressible flow

(D)

any two points along a streamline for steady incompressible rotational flow

Explanation

GATE→2026→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q4

MCQ[1 Mark]

A hydraulic crane supports a mass of $500~kg$ with its piston-cylinder actuator, inclined at $60^{\circ}$ with horizontal, as shown in the figure below. The diameter of the piston is $30~cm$ and gravitational acceleration is $10~m/s^{2}$. Neglecting mass of the piston, the reading of the pressure gage in kPa (gage) is

(A)

61.26

(B)

6.13

(C)

35.35

(D)

70.71

Explanation

GATE→2026→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q5

NAT[2 Marks]

Water with a density of $1000~kg/m^{3}$ comes out of an industrial condenser through a horizontal pipe of $15~cm$ radius at the flow rate of $4.5~m^{3}/min$. The outlet of the pipe is connected to a coaxial diffuser of $0.5~m$ length using a flange to raise the pressure of water to atmospheric condition without any backflow. The inner radius ($r$, in $m$) of the diffuser cross-section is expressed as $r=0.15+0.4~x^{2}$ where, $x$ represents the axial distance of the diffuser in m, from its inlet. Considering frictionless flow, the magnitude of the force exerted by the diffuser on the flange is ____ N (rounded off to 2 decimal places).

Explanation

GATE→2025→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q6

MCQ[1 Mark]

Consider two identical tanks with a bottom hole of diameter $d$. One tank is filled with water and the other tank is filled with engine oil. The height of the fluid column $h$ is same in both the cases. The fluid exit velocity in the two tanks are $V_{1}$ and $V_{2}$. Neglecting all losses, which one of the following options is correct?

(A)

V_{2} > V_{1}

(B)

V_{2} = V_{1}

(C)

V_{2} < V_{1}

(D)

Insufficient data to definitively conclude relationship between V_1 and V_2

Explanation

GATE→2025→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q7

MCQ[1 Mark]

In a laboratory experiment using a scaled down model to measure scour at a bridge pier, the Froude number is important. The ratio of the prototype length to the model length is $100$. If the velocity of the model is $1~m~s^{-1}$, the velocity (in $m~s^{-1}$) of the prototype is

(A)

0.1

(B)

1

(C)

10

(D)

100

Explanation

GATE→2025→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q8

MSQ[2 Marks]

For a fully-developed pipe flow, which of the following options is/are correct?

(A)

For the same maximum velocity, the average velocity is higher in the turbulent regime than that of the laminar regime

(B)

Compressibility effects are important if Mach number is less than 0.3

(C)

For laminar flow, the friction factor is independent of surface roughness

(D)

For laminar flow, friction factor decreases with decrease in Reynolds number

Explanation

GATE→2025→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q9

NAT[2 Marks]

A pitot tube connected to a U-tube mercury manometer measures the speed of air flowing in the wind tunnel as shown in the figure below. The density of air is $1.23~kg~m^{-3}$ while the density of water is $1000~kg~m^{-3}$. For the manometer reading of $h=30~mm$ of mercury, the speed of air in the wind tunnel is ____ $m~s^{-1}$ (rounded off to 1 decimal place).\nAssume: Specific gravity of mercury $=13.6$, Acceleration due to gravity $=10~m~s^{-2}$

Explanation

GATE→2025→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q10

NAT[2 Marks]

Consider a velocity field $\vec{V}=3z\hat{i}+0\hat{j}+Cx\hat{k}$, where $C$ is a constant. If the flow is irrotational, the value of $C$ is ____ (rounded off to 1 decimal place).

Explanation

GATE→2024→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q11

MCQ[1 Mark]

The velocity field of a two-dimensional, incompressible flow is given by $$\vec{V}=2~\sinh x\hat{i}+v(x,y)\hat{j}$$\nwhere $\hat{i}$ and $\hat{j}$ denote the unit vectors in $x$ and $y$ directions, respectively. If $v(x,0)=\cosh x$, then $v(0,-1)$ is

(A)

1

(B)

2

(C)

3

(D)

4

Explanation

GATE→2024→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q12

MCQ[2 Marks]

In the pipe network shown in the figure, all pipes have the same cross-section and can be assumed to have the same friction factor. The pipes connecting points W, N, and S with point J have an equal length L. The pipe connecting points J and E has a length 10L. The pressures at the ends N, E, and S are equal. The flow rate in the pipe connecting W and J is Q. Assume that the fluid flow is steady, incompressible, and the pressure losses at the pipe entrance and junction are negligible. Consider the following statements:\nI: The flow rate in pipe connecting J and E is Q/21.\nII: The pressure difference between J and N is equal to the pressure difference between J and E.\nWhich one of the following options is CORRECT?

(A)

Statement I is True and Statement II is False

(B)

Both I and II are True

(C)

Both I and II are False

(D)

Statement I is False and Statement II is True

Explanation

GATE→2024→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q13

MSQ[2 Marks]

Steady, compressible flow of air takes place through an adiabatic converging-diverging nozzle, as shown in the figure. For a particular value of pressure difference across the nozzle, a stationary normal shock wave forms in the diverging section of the nozzle. If E and F denote the flow conditions just upstream and downstream of the normal shock, respectively, which of the following statement(s) is/are TRUE?

(A)

Static pressure at E is lower than static pressure at F

(B)

Density at E is lower than density at F

(C)

Mach number at E is lower than Mach number at F

(D)

Specific entropy at E is lower than specific entropy at F

Explanation

GATE→2024→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q14

NAT[2 Marks]

A liquid fills a horizontal capillary tube whose one end is dipped in a large pool of the liquid. Experiments show that the distance $L$ travelled by the liquid meniscus in time $t$ is given by $$L=k\gamma^{a}R^{b}\mu^{c}\sqrt{t}$$\nwhere $\gamma$ is the surface tension, $R$ is the inner radius of the capillary, and $\mu$ is the dynamic viscosity of the liquid. If $k$ is a dimensionless constant, then the value of $a$ is ____ (rounded off to 1 decimal place).

Explanation

GATE→2023→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q15

MCQ[1 Mark]

Air (density $=1.2~kg/m^{3}$, kinematic viscosity $=1.5\times 10^{-5}m^{2}/s$) flows over a flat plate with a free-stream velocity of $2~m/s$. The wall shear stress at a location $15~mm$ from the leading edge is $\tau_{w}$. What is the wall shear stress at a location $30~mm$ from the leading edge?

(A)

\tau_{w}/2

(B)

\sqrt{2}\tau_{w}

(C)

2~\tau_{w}

(D)

\tau_{w}/\sqrt{2}

Explanation

GATE→2023→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q16

MCQ[1 Mark]

Consider an isentropic flow of air (ratio of specific heats $=1.4$) through a duct as shown in the figure. The variations in the flow across the cross-section are negligible. The flow conditions at Location 1 are given as follows: $P_{1}=100~kPa$, $\rho_{1}=1.2~kg/m^{3}$, $u_{1}=400~m/s$\nThe duct cross-sectional area at Location 2 is given by $A_{2}=2A_{1}$, where $A_{1}$ denotes the duct cross-sectional area at Location 1. Which one of the given statements about the velocity $u_{2}$ and pressure $P_{2}$ at Location 2 is TRUE?

(A)

u_2 < u_1, P_2 < P_1

(B)

u_2 < u_1, P_2 > P_1

(C)

u_2 > u_1, P_2 < P_1

(D)

u_2 > u_1, P_2 > P_1

Explanation

GATE→2023→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q17

NAT[2 Marks]

The velocity field of a certain two-dimensional flow is given by $$\vec{V}(x,y)=k(x\hat{i}-y\hat{j})$$\nwhere $k=2~s^{-1}$. The coordinates $x$ and $y$ are in meters. Assume gravitational effects to be negligible.\nIf the density of the fluid is $1000~kg/m^{3}$ and the pressure at the origin is $100~kPa$, the pressure at the location $(2~m, 2~m)$ is ____ kPa. (Answer in integer)

Explanation

GATE→2023→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q18

NAT[2 Marks]

Consider a unidirectional fluid flow with the velocity field given by $$V(x,y,z,t)=u(x,t)\hat{i}$$\nwhere $u(0,t)=1$. If the spatially homogeneous density field varies with time $t$ as $$\rho(t)=1+0.2e^{-t}$$\nthe value of $u(2,1)$ is ____ (Rounded off to two decimal places)\nAssume all quantities to be dimensionless.

Explanation

GATE→2023→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q19

NAT[2 Marks]

The figure shows two fluids held by a hinged gate. The atmospheric pressure is $P_{a}=100~kPa$. The moment per unit width about the base of the hinge is ____ kNm/m. (Rounded off to one decimal place)\nTake the acceleration due to gravity to be $g=9.8~m/s^{2}$.

Explanation

GATE→2023→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q20

NAT[2 Marks]

An explosion at time $t=0$ releases energy $E$ at the origin in space filled with a gas of density $\rho$. Subsequently, a hemispherical blast wave propagates radially outwards as shown in the figure. Let $R$ denote the radius of the front of the hemispherical blast wave. The radius $R$ follows the relationship $R=k~t^{a}E^{b}\rho^{c}$ where $k$ is a dimensionless constant. The value of exponent $a$ is ____ (Rounded off to one decimal place)

Explanation

GATE→2022→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q21

MCQ[1 Mark]

A tiny temperature probe is fully immersed in a flowing fluid and is moving with zero relative velocity with respect to the fluid. The velocity field in the fluid is 𝑽ሬ⃗= (2𝑥)ଙ̂ + (𝑦+ 3𝑡)ଚ̂, and the temperature field in the fluid is 𝑇= 2𝑥ଶ+ 𝑥𝑦+ 4𝑡, where x and y are the spatial coordinates, and t is the time. The time rate of change of temperature recorded by the probe at (𝑥= 1, 𝑦= 1, 𝑡= 1) is _______. (A) 4 (B) 0 (C) 18 (D) 14

(A)

4

(B)

0

(C)

18

(D)

14

Explanation

GATE→2022→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q22

MCQ[1 Mark]

In the following two-dimensional momentum equation for natural convection over a surface immersed in a quiescent fluid at temperature 𝑇ஶ (𝑔 is the gravitational acceleration, 𝛽 is the volumetric thermal expansion coefficient, 𝝂 is the kinematic viscosity, 𝑢 and 𝑣 are the velocities in 𝑥 and 𝑦 directions, respectively, and T is the temperature) 𝑢 డ௨ డ௫+ 𝑣 డ௨ డ௬= 𝑔𝛽(𝑇−𝑇ஶ) + 𝝂 డమ௨ డ௬మ , the term 𝑔𝛽(𝑇−𝑇ஶ) represents (A) Ratio of inertial force to viscous force. (B) Ratio of buoyancy force to viscous force. (C) Viscous force per unit mass. (D) Buoyancy force per unit mass.

(A)

Ratio of inertial force to viscous force.

(B)

Ratio of buoyancy force to viscous force.

(C)

Viscous force per unit mass.

(D)

Buoyancy force per unit mass.

Explanation

GATE→2022→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q23

MSQ[1 Mark]

The figure shows a purely convergent nozzle with a steady, inviscid compressible flow of an ideal gas with constant thermophysical properties operating under choked condition. The exit plane shown in the figure is located within the nozzle. If the inlet pressure (P0) is increased while keeping the back pressure (Pback) unchanged, which of the following statements is/are true? (A) Mass flow rate through the nozzle will remain unchanged. (B) Mach number at the exit plane of the nozzle will remain unchanged at unity. (C) Mass flow rate through the nozzle will increase. (D) Mach number at the exit plane of the nozzle will become more than unity.

(A)

Mass flow rate through the nozzle will remain unchanged.

(B)

Mach number at the exit plane of the nozzle will remain unchanged at unity.

(C)

Mass flow rate through the nozzle will increase.

(D)

Mach number at the exit plane of the nozzle will become more than unity.

Explanation

GATE→2022→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q24

MCQ[2 Marks]

A solid spherical bead of lead (uniform density = 11000 kg/m3) of diameter d = 0.1 mm sinks with a constant velocity V in a large stagnant pool of a liquid (dynamic viscosity = 1.1 × 10ିଷ kg∙m∙s). The coefficient of drag is given by 𝑐஽= ଶସ ୖୣ, where the Reynolds number (Re) is defined on the basis of the diameter of the bead. The drag force acting on the bead is expressed as 𝐷= (𝑐஽)(0.5𝜌𝑉ଶ) ቀ గௗమ ସቁ, where ρ is the density of the liquid. Neglect the buoyancy force. Using 𝑔= 10 m/s2, the velocity V is __________ m/s. (A) 1 24 (B) 1 6 (C) 1 18 (D) 1 12

(A)

1 24

(B)

1 6

(C)

1 18

(D)

1 12

Explanation

GATE→2022→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q25

MCQ[2 Marks]

Consider steady, one-dimensional compressible flow of a gas in a pipe of diameter 1 m. At one location in the pipe, the density and velocity are 1 kg/m3 and 100 m/s, respectively. At a downstream location in the pipe, the velocity is 170 m/s. If the pressure drop between these two locations is 10 kPa, the force exerted by the gas on the pipe between these two locations is ____________ N. (A) 350𝜋ଶ (B) 750π (C) 1000π (D) 3000

(A)

350𝜋ଶ

(B)

750π

(C)

1000π

(D)

3000

Explanation

GATE→2022→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q26

NAT[2 Marks]

In a steam power plant based on Rankine cycle, steam is initially expanded in a high-pressure turbine. The steam is then reheated in a reheater and finally expanded in a low-pressure turbine. The expansion work in the high-pressure turbine is 400 kJ/kg and in the low-pressure turbine is 850 kJ/kg, whereas the pump work is 15 kJ/kg. If the cycle efficiency is 32%, the heat rejected in the condenser is ________ kJ/kg (round off to 2 decimal places).

Explanation

GATE→2022→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q27

NAT[2 Marks]

A steady two-dimensional flow field is specified by the stream function 𝜓= 𝑘𝑥ଷ𝑦, where 𝑥 and 𝑦 are in meter and the constant 𝑘 = 1 ms. The magnitude of acceleration at a point (x, y) = (1 m, 1 m) is ________ m/s2 (round off to 2 decimal places).

Explanation

GATE→2022→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q28

NAT[2 Marks]

Consider a solid slab (thermal conductivity, k = 10 W∙m∙K) with thickness 0.2 m and of infinite extent in the other two directions as shown in the figure. Surface 2, at 300 K, is exposed to a fluid flow at a free stream temperature (T∞) of 293 K, with a convective heat transfer coefficient (h) of 100 W∙m∙K. Surface 2 is opaque, diffuse and gray with an emissivity () of 0.5 and exchanges heat by radiation with very large surroundings at 0 K. Radiative heat transfer inside the solid slab is neglected. The Stefan-Boltzmann constant is 5.67×108 W∙m∙K. The temperature T1 of Surface 1 of the slab, under steady-state conditions, is _________ K (round off to the nearest integer).

Explanation

GATE→2022→Fluid Mechanics and Thermal Sciences→Fluid Mechanics

Q29

NAT[2 Marks]

During open-heart surgery, a patient’s blood is cooled down to 25 C from 37 C using a concentric tube counter-flow heat exchanger. Water enters the heat exchanger at 4 C and leaves at 18 C. Blood flow rate during the surgery is 5 L/minute. Use the following fluid properties: Fluid Density (kg/m3) Specific heat (J/kg-K) Blood 1050 3740 Water 1000 4200 Effectiveness of the heat exchanger is _________ (round off to 2 decimal places).

Explanation

Heat Transfer

23 Questions

GATE→2026→Fluid Mechanics and Thermal Sciences→Heat Transfer

Q30

MCQ[1 Mark]

A quiescent fluid at temperature $T_{3}$ is confined between two vertical parallel plates. While plate 1 is kept at temperature $T_{1}$ and plate 2 is maintained at temperature $T_{2}$, a velocity profile between the plates, as shown in the figure below, is generated due to heat transfer. Which one of the following options shows the correct relations among $T_{1}$, $T_{2}$, and $T_{3}$?

(A)

T_{1}>T_{3} \text{ and } T_{3}>T_{2}

(B)

T_{1}>T_{3} \text{ and } T_{3}<T_{2}

(C)

T_{1}<T_{3} \text{ and } T_{3}<T_{2}

(D)

T_{1}<T_{3} \text{ and } T_{3}>T_{2}

Explanation

GATE→2026→Fluid Mechanics and Thermal Sciences→Heat Transfer

Q31

NAT[1 Mark]

A sphere of radius $5~mm$ is initially in equilibrium at $400^{\circ}C$ in a furnace. It is suddenly removed from the furnace and dipped in a well-stirred water bath at $20^{\circ}C$, with a convection heat transfer coefficient of $500~W/(m^{2}K)$. For the given range of temperatures, the thermophysical properties of the material of the sphere are: density $\rho=3000~kg/m^{3}$, thermal conductivity $k=10~W/(m~K)$, and specific heat $c=1000~J/(kg~K)$. Neglecting radiation heat transfer, the time required for the centre of the sphere to cool from $400^{\circ}C$ to $50^{\circ}C$ is ____ seconds (rounded off to 2 decimal places).

Explanation

GATE→2026→Fluid Mechanics and Thermal Sciences→Heat Transfer

Q32

MCQ[2 Marks]

A very long fin of a uniform square cross-section is replaced by another very long fin of a uniform circular cross-section of the same material. Assume uniform and identical heat transfer coefficient for both the fins. If the diameter of ket circular fin is equal to the side length of the square fin, then the ratio of heat transfer rates before and after the replacement is

(A)

\frac{4}{\pi}

(B)

\frac{16}{\pi^{2}}

(C)

\frac{1}{\pi}

(D)

\frac{1}{\pi^{2}}

Explanation

GATE→2026→Fluid Mechanics and Thermal Sciences→Heat Transfer

Q33

NAT[2 Marks]

Two rectangular surfaces both having $1~m^{2}$ area are placed perpendicular to each other with a common edge. One surface is hot, having a temperature of $1000~K$ and emissivity of $0.4$, while the other is insulated and in radiant balance with a large surrounding room at $300~K$. If the fraction of radiation leaving the hot surface which reaches the cold surface is $0.2$, then the equivalent overall resistance for the radiation heat loss from the hot surface is ____ $m^{-2}$ (rounded off to 2 decimal places).

Explanation

GATE→2026→Fluid Mechanics and Thermal Sciences→Heat Transfer

Q34

NAT[2 Marks]

Convective heat transfer coefficients for Fluid 1 and Fluid 2 in a heat exchanger, as shown in the figure below, are $50~W/(m^{2}K)$ and $80~W/(m^{2}K)$, respectively. The inner tube is made of a material which has a thermal conductivity $386~W/(m~K)$ for the given range of temperatures in the heat exchanger. The length of the heat exchanging surface, the inside radius of the inner tube, and thickness of the inner tube are $1~m$, $10~mm$, and $1~mm$, respectively. Considering no heat exchange between the outer tube and the surrounding, the heat transfer rate for the heat exchanger is ____ W (rounded off to 1 decimal place).

Explanation

GATE→2025→Fluid Mechanics and Thermal Sciences→Heat Transfer

Q35

MCQ[1 Mark]

Let a spherical block of ice at $-7^{\circ}C$ be exposed to atmospheric air at $30^{\circ}C$ with the gravitational direction as shown in the figure below. What will be the overall direction of air flow in this situation?

(A)

Upward

(B)

Downward

(C)

NO motion

(D)

Sideward

Explanation

GATE→2025→Fluid Mechanics and Thermal Sciences→Heat Transfer

Q36

NAT[2 Marks]

Consider a cylindrical furnace of $5~m$ diameter and $5~m$ length with bottom, top and curved surfaces maintained at uniform temperatures of $800~K$, $1500~K$ and $500~K$, respectively. The view factor between the bottom and top surfaces, $F_{12}$ is $0.2$. The magnitude of net radiation heat transfer rate between the bottom surface and the curved surface is ____ kW (rounded off to 1 decimal place).\nAll surfaces of the furnace can be assumed as black.\nThe Stefan-Boltzmann constant, $\sigma=5.67\times 10^{-8}~W~m^{-2}K^{-4}$.

Explanation

GATE→2025→Fluid Mechanics and Thermal Sciences→Heat Transfer

Q37

NAT[2 Marks]

Water enters a tube of diameter, $D=60~mm$ with mass flow rate of $0.01~kg~s^{-1}$ as shown in the figure below. The inlet mean temperature is $T_{m,i}=293~K$ and the uniform heat flux at the surface of the tube is $2000~W~m^{-2}$. For the exit mean temperature of $T_{m,o}=353~K$, the length of the tube, $L$ is ____ m (rounded off to 1 decimal place).\nUse the specific heat of water as $4181~J~kg^{-1}K^{-1}$.

Explanation

GATE→2024→Fluid Mechanics and Thermal Sciences→Heat Transfer

Q38

MCQ[1 Mark]

A plane, solid slab of thickness L, shown in the figure, has thermal conductivity $k$ that varies with the spatial coordinate $x$ as $k=A+Bx$, where $A$ and $B$ are positive constants ($A>0, B>0$). The slab walls are maintained at fixed temperatures of $T(x=0)=0$ and $T(x=L)=T_{0}>0$. The slab has no internal heat sources. Considering one-dimensional heat transfer, which one of the following plots qualitatively depicts the steady-state temperature distribution within the slab?

(A)

A

(B)

B

(C)

C

(D)

D

Explanation

GATE→2024→Fluid Mechanics and Thermal Sciences→Heat Transfer

Q39

MCQ[1 Mark]

Consider incompressible laminar flow over a flat plate with freestream velocity of $u_{\infty}$. The Nusselt number corresponding to this flow velocity is $Nu_{1}$. If the freestream velocity is doubled, the Nusselt number changes to $Nu_{2}$. Choose the correct option for $Nu_{2}/Nu_{1}$.

(A)

\sqrt{2}

(B)

2

(C)

1.26

(D)

1

Explanation

GATE→2024→Fluid Mechanics and Thermal Sciences→Heat Transfer

Q40

MCQ[1 Mark]

Consider a hydrodynamically fully developed laminar flow through a circular pipe with the flow along the axis (i.e., $z$ direction). In the following statements, $T$ is the temperature of the fluid, $T_{w}$ is the wall temperature and $T_{m}$ is the bulk mean temperature of the fluid. Which one of the following statements is TRUE? [Note: Official Key marked this as MTA (Marks To All)]

(A)

For a thermally fully developed flow, \frac{\partial T}{\partial z} = 0 always

(B)

For constant wall temperature of duct, \frac{dT_m}{dz} = constant

(C)

Nusselt number varies linearly along z direction for thermally fully developed flow

(D)

For constant wall temperature (T_w > T_m), \frac{dT_m}{dz} increases exponentially with distance along z

Explanation

GATE→2024→Fluid Mechanics and Thermal Sciences→Heat Transfer

Q41

NAT[2 Marks]

Consider a slab of $20~mm$ thickness. There is a uniform heat generation of $\dot{q}=100~MW/m^{3}$ inside the slab. The left and right faces of the slab are maintained at $150^{\circ}C$ and $110^{\circ}C$, respectively. The plate has a constant thermal conductivity of $200~W/(m \cdot K)$. Considering a 1-D steady state heat conduction, the location of the maximum temperature from the left face will be at ____ mm (answer in integer).

Explanation

GATE→2024→Fluid Mechanics and Thermal Sciences→Heat Transfer

Q42

NAT[2 Marks]

A condenser is used as a heat exchanger in a large steam power plant in which steam is condensed to liquid water. The condenser is a shell and tube heat exchanger which consists of 1 shell and 20,000 tubes. Water flows through each of the tubes at a rate of $1~kg/s$ with an inlet temperature of $30^{\circ}C$. The steam in the condenser shell condenses at the rate of $430~kg/s$ at a temperature of $50^{\circ}C$. If the heat of vaporization is $2.326~MJ/kg$ and specific heat of water is $4~kJ/(kg \cdot K)$, the effectiveness of the heat exchanger is ____ (rounded off to 3 decimal places).

Explanation

GATE→2024→Fluid Mechanics and Thermal Sciences→Heat Transfer

Q43

NAT[2 Marks]

Consider a hemispherical furnace of diameter $D=6~m$ with a flat base. The dome of the furnace has an emissivity of $0.7$ and the flat base is a blackbody. The base and the dome are maintained at uniform temperature of $300~K$ and $1200~K$, respectively. Under steady state conditions, the rate of radiation heat transfer from the dome to the base is ____ kW (rounded off to 1 decimal place).\nUse Stefan-Boltzmann constant $=5.67\times 10^{-8}~W/(m^{2}K^{4})$

Explanation

GATE→2023→Fluid Mechanics and Thermal Sciences→Heat Transfer

Q44

MCQ[1 Mark]

Consider incompressible laminar flow of a constant property Newtonian fluid in an isothermal circular tube. The flow is steady with fully-developed temperature and velocity profiles. The Nusselt number for this flow depends on

(A)

neither Reynolds nor Prandtl number

(B)

both Reynolds and Prandtl numbers

(C)

Reynolds number but not Prandtl number

(D)

Prandtl number but not Reynolds number

Explanation

GATE→2023→Fluid Mechanics and Thermal Sciences→Heat Transfer

Q45

MSQ[1 Mark]

Consider a laterally insulated rod of length L and constant thermal conductivity. Assuming one-dimensional heat conduction in the rod, which of the following steady-state temperature profile(s) can occur without internal heat generation?

(A)

A

(B)

B

(C)

C

(D)

D

Explanation

GATE→2023→Fluid Mechanics and Thermal Sciences→Heat Transfer

Q46

NAT[1 Mark]

Consider a counter-flow heat exchanger with the inlet temperatures of two fluids (1 and 2) being $T_{1,in}=300~K$ and $T_{2,in}=350~K$. The heat capacity rates of the two fluids are $C_{1}=1000~W/K$ and $C_{2}=400~W/K$ and the effectiveness of the heat exchanger is $0.5$. The actual heat transfer rate is ____ kW. (Answer in integer)

Explanation

GATE→2023→Fluid Mechanics and Thermal Sciences→Heat Transfer

Q47

MCQ[2 Marks]

A cylindrical rod of length $h$ and diameter $d$ is placed inside a cubic enclosure of side length $L$. S denotes the inner surface of the cube. The view-factor $F_{S-S}$ is

(A)

0

(B)

1

(C)

(\pi dh + \pi d^2 / 2) / (6 L^2)

(D)

1 - \frac{(\pi dh + \pi d^2 / 2)}{6 L^2}

Explanation

GATE→2023→Fluid Mechanics and Thermal Sciences→Heat Transfer

Q48

MSQ[2 Marks]

A very large metal plate of thickness d and thermal conductivity k is cooled by a stream of air at temperature $T_{\infty}=300~K$ with a heat transfer coefficient h, as shown in the figure. The centerline temperature of the plate is $T_{P}$. In which of the following case(s) can the lumped parameter model be used to study the heat transfer in the metal plate?

(A)

h = 10 W/m^2K, k = 100 W/mK, d = 1 mm, T_P = 350 K

(B)

h = 100 W/m^2K, k = 100 W/mK, d = 1 m, T_P = 325 K

(C)

h = 100 W/m^2K, k = 1000 W/mK, d = 1 mm, T_P = 325 K

(D)

h = 1000 W/m^2K, k = 1 W/mK, d = 1 m, T_P = 350 K

Explanation

GATE→2022→Fluid Mechanics and Thermal Sciences→Heat Transfer

Q49

MCQ[2 Marks]

In Fe-Fe3C phase diagram, the eutectoid composition is 0.8 weight % of carbon at 725 ºC. The maximum solubility of carbon in α-ferrite phase is 0.025 weight % of carbon. A steel sample, having no other alloying element except 0.5 weight % of carbon, is slowly cooled from 1000 ºC to room temperature. The fraction of pro-eutectoid α-ferrite in the above steel sample at room temperature is (A) 0.387 (B) 0.864 (C) 0.475 (D) 0.775

(A)

0.387

(B)

0.864

(C)

0.475

(D)

0.775

Explanation

GATE→2022→Fluid Mechanics and Thermal Sciences→Heat Transfer

Q50

NAT[2 Marks]

Two mild steel plates of similar thickness, in butt-joint configuration, are welded by gas tungsten arc welding process using the following welding parameters. Welding voltage 20 V Welding current 150 A Welding speed 5 mm/s A filler wire of the same mild steel material having 3 mm diameter is used in this welding process. The filler wire feed rate is selected such that the final weld bead is composed of 60% volume of filler and 40% volume of plate material. The heat required to melt the mild steel material is 10 J/mm3. The heat transfer factor is 0.7 and melting factor is 0.6. The feed rate of the filler wire is __________ mm/s (round off to one decimal place).

Explanation

GATE→2022→Fluid Mechanics and Thermal Sciences→Heat Transfer

Q51

NAT[2 Marks]

Consider a one-dimensional steady heat conduction process through a solid slab of thickness 0.1 m. The higher temperature side A has a surface temperature of 80 C, and the heat transfer rate per unit area to low temperature side B is 4.5 kW/m2. The thermal conductivity of the slab is 15 W/m.K. The rate of entropy generation per unit area during the heat transfer process is ________ W/m2.K (round off to 2 decimal places).

Explanation

GATE→2022→Fluid Mechanics and Thermal Sciences→Heat Transfer

Q52

NAT[2 Marks]

An engine running on an air standard Otto cycle has a displacement volume 250 cm3 and a clearance volume 35.7 cm3. The pressure and temperature at the beginning of the compression process are 100 kPa and 300 K, respectively. Heat transfer during constant-volume heat addition process is 800 kJ/kg. The specific heat at constant volume is 0.718 kJ/kg.K and the ratio of specific heats at constant pressure and constant volume is 1.4. Assume the specific heats to remain constant during the cycle. The maximum pressure in the cycle is ______ kPa (round off to the nearest integer).

Explanation

Thermodynamics

16 Questions

GATE→2026→Fluid Mechanics and Thermal Sciences→Thermodynamics

Q53

MCQ[1 Mark]

For an ideal gas, starting from state point 1, two different processes take place. The corresponding final states in these two processes are 2 and 3, lying on same isotherm. If P and h represent pressure and enthalpy, respectively, then which one of the following options is correct?

(A)

h_{2}=h_{3}

(B)

h_{2}>h_{3}

(C)

P_{2}h_{3}=P_{3}h_{2}

(D)

P_{3}h_{3}=P_{2}h_{2}

Explanation

GATE→2026→Fluid Mechanics and Thermal Sciences→Thermodynamics

Q54

MCQ[1 Mark]

For the isothermal expansion of an ideal gas in a piston cylinder system, the net heat supplied during the process is equal to the net work. Which one of the following statements is correct for the given process?

(A)

The process is possible.

(B)

The process is not possible as it violates the second law of thermodynamics.

(C)

The process is not possible as it violates the first law of thermodynamics.

(D)

The process is possible, however, it violates the second law of thermodynamics.

Explanation

GATE→2026→Fluid Mechanics and Thermal Sciences→Thermodynamics

Q55

NAT[2 Marks]

A liquid comes out of the reactor of a chemical plant at $250^{\circ}C$ temperature with a flow rate of $100~LPM$. The ambient temperature is $25^{\circ}C$. Density and specific heat of the liquid remain constant at $1000~kg/m^{3}$ and $4.18~kJ/(kg~K)$, respectively, for the given range of temperature. The rate of exergy associated with the hot liquid stream at the exit of the plant is ____ kW (rounded off to 2 decimal places).

Explanation

GATE→2026→Fluid Mechanics and Thermal Sciences→Thermodynamics

Q56

NAT[2 Marks]

A rigid closed vertical cylindrical vessel of $15~cm$ diameter contains $5~kg$ water at $80^{\circ}C$ with $10\%$ quality. The water is heated till its temperature reaches $130^{\circ}C$. Considering only a horizontal separated interface between liquid and vapor, the dip in the liquid level after heating process is ____ cm (rounded off to 2 decimal places).

Explanation

GATE→2025→Fluid Mechanics and Thermal Sciences→Thermodynamics

Q57

MCQ[1 Mark]

Air inside a rigid, thermally-insulated tank undergoes stirring as shown in the figure below. Which one of the following options is correct?

(A)

The enthalpy of the air increases while the entropy of the air remains constant

(B)

Both the enthalpy and the entropy of the air remain constant

(C)

Both the enthalpy and the entropy of the air increase

(D)

The enthalpy of the air decreases while the entropy of the air increases

Explanation

GATE→2025→Fluid Mechanics and Thermal Sciences→Thermodynamics

Q58

NAT[2 Marks]

A thermodynamically closed system contains $1~kg$ of hydrogen. The system undergoes a reversible polytropic process with polytropic index $1.3$. The work output during the process is $400~kJ$. During the process, hydrogen behaves as an ideal gas with constant specific heats. The absolute value of heat transfer during the process is ____ kJ (rounded off to 1 decimal place).\nSpecific heat of hydrogen at constant pressure $= 14.56~kJ~kg^{-1}K^{-1}$\nSpecific heat of hydrogen at constant volume $= 10.4~kJ~kg^{-1}K^{-1}$

Explanation

GATE→2024→Fluid Mechanics and Thermal Sciences→Thermodynamics

Q59

MCQ[1 Mark]

A furnace can supply heat steadily at $1200~K$ at a rate of $24000~kJ/min$. The maximum amount of power (in kW) that can be produced by using the heat supplied by this furnace in an environment at $300~K$ is

(A)

300

(B)

150

(C)

18000

(D)

0

Explanation

GATE→2024→Fluid Mechanics and Thermal Sciences→Thermodynamics

Q60

MCQ[1 Mark]

Which one of the following statements regarding a Rankine cycle is FALSE?

(A)

Superheating steam in boiler increases cycle efficiency

(B)

Pressure at turbine outlet depends on condenser temperature

(C)

Cycle efficiency increases as condenser pressure decreases

(D)

Cycle efficiency increases as boiler pressure decreases

Explanation

GATE→2024→Fluid Mechanics and Thermal Sciences→Thermodynamics

Q61

NAT[2 Marks]

A piston-cylinder arrangement shown in the figure has a stop located $2~m$ above the base. The cylinder initially contains air at $140~kPa$ and $350^{\circ}C$ and the piston is resting in equilibrium at a position which is $1~m$ above the stops ($3~m$ total height). The system is now cooled to the ambient temperature of $25^{\circ}C$. Consider air to be an ideal gas with a value of gas constant $R=0.287~kJ/(kg \cdot K)$.\nThe absolute value of specific work done during the process is ____ kJ/kg (rounded off to 1 decimal place).

Explanation

GATE→2024→Fluid Mechanics and Thermal Sciences→Thermodynamics

Q62

NAT[2 Marks]

A heat pump (H.P.) is driven by the work output of a heat engine (H.E.) as shown in the figure. The heat engine extracts $150~kJ$ of heat from the source at $1000~K$. The heat pump absorbs heat from the ambient at $280~K$ and delivers heat to the room which is maintained at $300~K$. Considering the combined system to be ideal, the total amount of heat delivered to the room together by the heat engine and heat pump is ____ kJ (answer in integer).

Explanation

GATE→2023→Fluid Mechanics and Thermal Sciences→Thermodynamics

Q63

MCQ[1 Mark]

A heat engine extracts heat $(Q_{H})$ from a thermal reservoir at a temperature of $1000~K$ and rejects heat $(Q_{L})$ to a thermal reservoir at a temperature of $100~K$, while producing work (W). Which one of the combinations of [$Q_{H}, Q_{L} \text{ and } W$] given is allowed?

(A)

Q_H = 2000 J, Q_L = 500 J, W = 1000 J

(B)

Q_H = 2000 J, Q_L = 750 J, W = 1250 J

(C)

Q_H = 6000 J, Q_L = 500 J, W = 5500 J

(D)

Q_H = 6000 J, Q_L = 600 J, W = 5500 J

Explanation

GATE→2023→Fluid Mechanics and Thermal Sciences→Thermodynamics

Q64

MCQ[2 Marks]

Which one of the following statements is FALSE?

(A)

For an ideal gas, enthalpy is independent of pressure

(B)

For real gas going through adiabatic reversible process, PV^\gamma = constant where \gamma is ratio of specific heats

(C)

For ideal gas undergoing reversible polytropic process PV^{1.5} = constant, equation connecting P, V, T is P/R = mT/V

(D)

Any real gas behaves as ideal gas at sufficiently low pressure or sufficiently high temperature

Explanation

GATE→2023→Fluid Mechanics and Thermal Sciences→Thermodynamics

Q65

MCQ[2 Marks]

Consider a fully adiabatic piston-cylinder arrangement as shown in the figure. The piston is massless and cross-sectional area of the cylinder is A. The fluid inside the cylinder is air (considered as a perfect gas), with $\gamma$ being the ratio of the specific heat at constant pressure to the specific heat at constant volume for air. The piston is initially located at a position $L_{1}$. The initial pressure of the air inside the cylinder is $P_{1}\gg P_{0}$ where $P_{0}$ is the atmospheric pressure. The stop $S_{1}$ is instantaneously removed and the piston moves to the position $L_{2}$, where the equilibrium pressure of air inside the cylinder is $P_{2}\gg P_{0}$.\nWhat is the work done by the piston on the atmosphere during this process?

(A)

0

(B)

P_0 A (L_2 - L_1)

(C)

P_1 A L_1 \ln(L_1 / L_2)

(D)

\frac{(P_2 L_2 - P_1 L_1)A}{1-\gamma}

Explanation

GATE→2023→Fluid Mechanics and Thermal Sciences→Thermodynamics

Q66

NAT[2 Marks]

Consider a mixture of two ideal gases, X and Y, with molar masses $\overline{M}_{X}=10~kg/kmol$ and $\overline{M}_{Y}=20~kg/kmol$, respectively, in a container. The total pressure in the container is $100~kPa$, the total volume of the container is $10~m^{3}$ and the temperature of the contents of the container is $300~K$. If the mass of gas-X in the container is $2~kg$, then the mass of gas-Y in the container is ____ kg. (Rounded off to one decimal place)\nAssume that the universal gas constant is $8314~J \cdot kmol^{-1}K^{-1}$.

Explanation

GATE→2022→Fluid Mechanics and Thermal Sciences→Thermodynamics

Q67

MCQ[1 Mark]

The Clausius inequality holds good for (A) any process (B) any cycle (C) only reversible process (D) only reversible cycle

(A)

any process

(B)

any cycle

(C)

only reversible process

(D)

only reversible cycle

Explanation

GATE→2022→Fluid Mechanics and Thermal Sciences→Thermodynamics

Q68

NAT[1 Mark]

A polytropic process is carried out from an initial pressure of 110 kPa and volume of 5 m3 to a final volume of 2.5 m3. The polytropic index is given by 𝑛= 1.2. The absolute value of the work done during the process is _______ kJ (round off to 2 decimal places).

Explanation

Applications (Power Engineering, I.C. Engines, Refrigeration, Turbomachinery)

8 Questions

GATE→2026→Fluid Mechanics and Thermal Sciences→Applications (Power Engineering, I.C. Engines, Refrigeration, Turbomachinery)

Q69

MCQ[2 Marks]

For an ideal regenerative Rankine cycle, as shown in the figure below, which one of the following options is the correct representation of temperature-entropy (T-s) diagram?

(A)

A

(B)

B

(C)

C

(D)

D

Explanation

GATE→2026→Fluid Mechanics and Thermal Sciences→Applications (Power Engineering, I.C. Engines, Refrigeration, Turbomachinery)

Q70

NAT[2 Marks]

An inward flow reaction turbine, having an outer diameter of $1~m$, runs at $600~RPM$. The normal component of absolute velocity at the inlet is $10~m/s$. If the guide blade angle is $15^{\circ}$, then the inlet vane angle of the runner is ____ degree (rounded off to 1 decimal place).

Explanation

GATE→2025→Fluid Mechanics and Thermal Sciences→Applications (Power Engineering, I.C. Engines, Refrigeration, Turbomachinery)

Q71

MCQ[1 Mark]

In a psychrometric chart, one axis represents dry-bulb temperature. The axis, that is perpendicular to the dry-bulb temperature axis, represents

(A)

wet-bulb temperature

(B)

specific humidity

(C)

relative humidity

(D)

enthalpy

Explanation

GATE→2025→Fluid Mechanics and Thermal Sciences→Applications (Power Engineering, I.C. Engines, Refrigeration, Turbomachinery)

Q72

NAT[1 Mark]

The thermal efficiency of an ideal air-standard Otto cycle is $0.5$. The value of specific heat ratio of air is $1.4$. The compression ratio of the cycle is ____ (rounded off to 1 decimal place).

Explanation

GATE→2025→Fluid Mechanics and Thermal Sciences→Applications (Power Engineering, I.C. Engines, Refrigeration, Turbomachinery)

Q73

NAT[2 Marks]

A thermal power plant is running with no reheat or regeneration. The specific enthalpy and specific entropy of steam at the turbine inlet are $3344~kJ~kg^{-1}$ and $6.5~kJ~kg^{-1}K^{-1}$ respectively. The turbine isentropic efficiency is $0.9$, and the mass flow rate of steam at the turbine inlet is $102~kg~s^{-1}$. The turbine power output is ____ MW (rounded off to 1 decimal place).

Explanation

GATE→2025→Fluid Mechanics and Thermal Sciences→Applications (Power Engineering, I.C. Engines, Refrigeration, Turbomachinery)

Q74

NAT[2 Marks]

Consider a Pelton wheel of $1~m$ diameter. The magnitude of relative velocity of water at the bucket inlet is same as the magnitude of relative velocity of water at the bucket exit. The absolute speed of water at the bucket inlet is $125.66~m~s^{-1}$. For maximum power output from the Pelton wheel, the rpm of the Pelton wheel is ____ (rounded off to 1 decimal place).

Explanation

GATE→2025→Fluid Mechanics and Thermal Sciences→Applications (Power Engineering, I.C. Engines, Refrigeration, Turbomachinery)

Q75

NAT[2 Marks]

A heat pump, operating in reversed Carnot cycle, maintains a steady air temperature of $300~K$ inside an auditorium. The heat pump receives heat from the ambient air. The ambient air temperature is $280~K$. Heat loss from the auditorium is $15~kW$. The power consumption of the heat pump is ____ kW (rounded off to 2 decimal places).

Explanation

GATE→2024→Fluid Mechanics and Thermal Sciences→Applications (Power Engineering, I.C. Engines, Refrigeration, Turbomachinery)

Q76

NAT[2 Marks]

Consider an air-standard Brayton cycle with adiabatic compressor and turbine, and a regenerator, as shown in the figure. Air enters the compressor at $100~kPa$ and $300~K$ and exits the compressor at $600~kPa$ and $550~K$. The air exits the combustion chamber at $1250~K$ and exits the adiabatic turbine at $100~kPa$ and $800~K$. The exhaust air from the turbine is used to preheat the air in the regenerator. The exhaust air exits the regenerator (state 6) at $600~K$. There is no pressure drop across the regenerator and the combustion chamber. Also, there is no heat loss from the regenerator to the surroundings. The ratio of specific heats at constant pressure and volume is $c_{p}/c_{v}=1.4$. The thermal efficiency of the cycle is ____ % (answer in integer).

Explanation