Heat Transfer Mechanical previous year questions with answer
Ques 31 GATE 2016 SET-1
A steel ball of 10 mm diameter at 1000 K is required to be cooled to 350 K by immersing it in a water environment at 300 K. The convective heat transfer coefficient is 1000 W/m2-K. Thermal conductivity of steel is 40 W/m-K. The time constant for the cooling process τ is 16 s. The time required (in s) to reach the final temperature is ________.
42.2 is the correct answer.
Ques 32 GATE 2016 SET-1
An infinitely long furnace of 0.5 m x 0.4 m cross-section is shown in the figure. Consider all surfaces of the furnace to be black. The top and bottom walls are maintained at temperature T1 = T3 = 927°C while the side walls are at temperature T2 = T4 = 527°C. The view factor, F1-2 is 0.26. The net radiation heat loss or gain on side 1 is ________ W/m. Stefan-Boltzmann constant = 5.67x10-8 W/m2-K4.
24530 is the correct answer.
Ques 33 GATE 2016 SET-1
A fluid (Prandtl number, Pr = 1) at 500 K flows over a flat plate of 1.5 m length, maintained at 300 K. The velocity of the fluid is 10 m/s. Assuming kinematic viscosity, ν = 30x10-6 m2/s, the thermal boundary layer thickness (in mm) at 0.5 m from the leading edge is ________.
6.12 is the correct answer.
Ques 34 GATE 2015 SET-2
The total emissive power of a surface is 500 W/m2 at a temperature T1 and 1200 W/m2 at a temperature T2, where the temperatures are in Kelvin. Assuming the emissivity of the surface to be constant, the ratio of the temperatures T1/T2 is
Ques 35 GATE 2015 SET-2
A balanced counterflow heat exchanger has a surface area of 20 m2 and overall heat transfer coefficient of 20 W/m2-K. Air (Cp = 1000 J/kg-K) entering at 0.4 kg/s and 280 K is to be preheated by the air leaving the system at 0.4 kg/s and 300 K. The outlet temperature (in K) of the preheated air is
Ques 36 GATE 2015 SET-2
A cylindrical uranium fuel rod of radius 5 mm in a nuclear reactor is generating heat at the rate of 4x107 W/m3. The rod is cooled by a liquid (convective heat transfer coefficient 1000 W/m2-K) at 25°C. At steady state, the surface temperature (in K) of the rod is
Ques 37 GATE 2015 SET-2
If a foam insulation is added to a 4 cm outer diameter pipe as shown in the figure, the critical radius of insulation (in cm) is ________.
5 is the correct answer.
Ques 38 GATE 2015 SET-2
In the laminar flow of air (Pr = 0.7) over a heated plate, if δ and δT denote, respectively, the hydrodynamic and thermal boundary layer thicknesses, then
Ques 39 GATE 2015 SET-1
For flow of viscous fluid over a flat plate, if the fluid temperature is the same as the plate temperature, the thermal boundary layer is
Ques 40 GATE 2015 SET-1
For flow through a pipe of radius R, the velocity and temperature distribution are as follows: u(r,x) = C1, and T(r,x) = C2[1 - (r/R)3], where C1 and C2 are constants. The bulk mean temperature is given by Tm = (2/(UmR2)) ∫0R u(r,x)T(r,x)rdr, with Um being the mean velocity of flow. The value of Tm is