ESE ME Heat Transfer : National Champion Test for ESE & GATE ME Exams

Question 1

A wall as shown below, is made up of two layers (A) and (B). The temperature are also shown in the sketch. The ratio of thermal conductivity of two layers is

=2

What is the ratio of thickness of two layers?

Question 2

A conduction heat flux of 25 kW/m²passes through a steel plate having thermal conductivity of 50 W/mK and thickness of 10 cm . If the temperature of the hot surface of the plate is 100⁰ C, then what is the temperature of the cooler side of the plate?

Question 3

A large concrete slab 1 m thick has one dimensional temperature distribution :

Where T is temperature and x is distance from one face towards other face of wall in meter. If the slab material has thermal diffusivity of

, what is the rate of change of temperature at the other face of the wall?

Question 4

There is a uniform distributed source of heat present in a plane wall whose one side (x=0) is insulated and other side (x=L) is exposed to ambient temperature (T), with heat transfer coefficient (h). Assuming constant thermal conductivity (k), steady state and one dimensional conduction, the temperature of the wall is maximum at x equal to

Question 5

Which non-dimensional number relates number relates the thermal boundary layer and hydrodynamic boundary layer?

Question 6

Given that Nu = Nusselt number,
Re = Reynolds number, Pr = Prandtl number
Sh = Sherwood number, Sc = Schmidt number, Gr = Grashoff number
The function relationship for free convective heat transfer is given as,

Question 7

For steady, uniform flow through pipes with constant heat flux supplied to the wall, what is the value of Nusseit number?

Question 8

For a fluid having Prandtl number equal to unity, how are the hydrodynamic boundary layer thickness (δ) and the thermal boundary layer thickness (δ_t) related ________?

Question 9

A thin flat plate 2 m x 2 m is hanging freely in air. The temperature of the the surroundings is

25°C. Solar radiation is falling on one side of the plate at the rate of 500 W. What should be the convection heat transfer coefficient in W/m²°C,(consider heat transfer only from the one surface) if the temperature of the plate is to remain constant at 30°C?

Question 10

If the radius of any current carrying conductor is less than the critical radius, then the addition of electrical insulation will enable the wire to carry a higher current because

Question 11

Consider steady-state heat conduction across the thickness in a plane composite wall (as shown in the figure) exposed to convection conditions on both sides.
Given: h_i = 20 W/m²K; h_o = 50 W/m²K; T_∞_,i= 20 °C: T_∞_,o= -2 °C; k₁ = 20 W/mK; k₂ = 50 W/mK; L₁ = 0.30 m and L₂ = 0.15 m. Assuming negligible contact resistance between the wall surfaces, the interface temperature, T (in °C), of the two walls will be

Question 12

A composite wall having three layers of thickness 0.3 m, 0.2 m and 0.1 m and of thermal conductivities 0.6, 0.4 and 0.1 W/mK respectively is having surface area 1 m². If the inner and outer temperature of the composite wall are 1840 k and 340 k , respectively, what is the rate of heat transfer?

Question 13

The equivalent thermal conductivity of the wall as shown in the figure below is

Question 14

A fin length l protrudes from a surface held at temperature T₀, it being higher than the ambient temperature T_a. The heat dissipation from the free end of the fin is sated to be negligibly small. What is the temperature gradient

at the tip of the fin?

Question 15

A fin will be more effective when Biot number is

Question 16

For a hemispherical furnace with a flat circular base of diameter D, the view factor from the dome to its base is

Question 17

Two radiating surfaces A₁ = 6 m² and A₂ = 4 m² have the shape factor F_1-2= 0.1 Then the value of F_2-1 will be

Question 18

Heat transfer through radiation takes place in form of:

Question 19

In a laminar developing flow through a pipe with constant wall temperature, the magnitude of the pipe wall inner surface convective heat transfer coefficient shall be maximum at the:

Question 20

The time constant of thermocouple is______.

Question 21

For the same inlet and outlet temperatures of hot and cold fluids, the Log Mean Temperature Difference (LMTD) is

Question 22

What is the net radiant interchange per square meter for two very large plates at temperatures 800 K and 500 K respectively. (The emissivity of the hot and cold plates are 0.8 abd 0.6 respectively. Stefan Boltzmann constant is 5.67 X

W/

).

Question 23

Consider a laminar boundary layer over a heated flat plate. The free stream velocity is $Description: D:\GradeStack Courses\GATE Tests (Sent by Ravi)\GATE ME-28-Mar\GATE-ME-2003_files\image243.png$ At some distance x from the leading edge the velocity boundary layer thickness is $Description: D:\GradeStack Courses\GATE Tests (Sent by Ravi)\GATE ME-28-Mar\GATE-ME-2003_files\image244.png$ and the thermal boundary layer thickness is $Description: D:\GradeStack Courses\GATE Tests (Sent by Ravi)\GATE ME-28-Mar\GATE-ME-2003_files\image245.png$ If the Prandtl number is greater than 1, then

Question 24

N_u = CR_e^mP_rⁿ represents heat transfer under

Question 25

A plate having 10 cm² area each side is hanging in the middle of a room of 100 m² total surface area. The plate temperature and emissivity are respectively 800 K and 0.6. the temperature and emissivity values for the surfaces of the room are 300K and 0.3 respectively. Boltzmann’s constant σ = 5.67 × 10^–8 W/m²K⁴. The total heat loss from the two surfaces of the plate is