Heat Transfer Mechanical previous year questions with answer
Ques 21 GATE 2017 SET-1
Heat is generated uniformly in a long solid cylindrical rod (diameter = 10 mm) at the rate of 4×107 W/m3. The thermal conductivity of the rod material is 25 W/m.K. Under steady state conditions, the temperature difference between the centre and the surface of the rod is ________ °C.
10 is the correct answer.
Ques 22 GATE 2017 SET-1
Two black surfaces, AB and BC, of lengths 5 m and 6 m, respectively, are oriented as shown. Both surfaces extend infinitely into the third dimension. Given that view factor F₁₂ = 0.5, T₁ = 800K, T₂ = 600K, T_surrounding = 300K and Stefan Boltzmann constant, σ = 5.67 × 10⁻⁸ W/(m²K⁴), the heat transfer rate from Surface 2 to the surrounding environment is ________ kW.
3.06 is the correct answer.
Ques 23 GATE 2016 SET-3
Steady one-dimensional heat conduction takes place across the faces 1 and 3 of a composite slab consisting of slabs A and B in perfect contact as shown in the figure, where kA, kB denote the respective thermal conductivities. Using the data as given in the figure, the interface temperature T2 (in °C) is ________.
67.5 is the correct answer.
Ques 24 GATE 2016 SET-3
Grashof number signifies the ratio of
Ques 25 GATE 2016 SET-3
For a heat exchanger, ΔTmax is the maximum temperature difference and ΔTmin is the minimum temperature difference between the two fluids. LMTD is the log mean temperature difference. Cmin and Cmax are the minimum and the maximum heat capacity rates. The maximum possible heat transfer (Qmax) between the two fluids is
Ques 26 GATE 2016 SET-2
A hollow cylinder has length L, inner radius r1, outer radius r2, and thermal conductivity k. The thermal resistance of the cylinder for radial conduction is
Ques 27 GATE 2016 SET-2
Consider the radiation heat exchange inside an annulus between two very long concentric cylinders. The radius of the outer cylinder is Ro and that of the inner cylinder is Ri. The radiation view factor of the outer cylinder onto itself is
Ques 28 GATE 2016 SET-2
Consider a parallel-flow heat exchanger with area Ap and a counter-flow heat exchanger with area Ac. In both the heat exchangers, the hot stream flowing at 1 kg/s cools from 80°C to 50°C. For the cold stream in both the heat exchangers, the flow rate and the inlet temperature are 2 kg/s and 10°C, respectively. The hot and cold streams in both the heat exchangers are of the same fluid. Also, both the heat exchangers have the same overall heat transfer coefficient. The ratio Ac/Ap is ________.
0.93 is the correct answer.
Ques 29 GATE 2016 SET-2
Two cylindrical shafts A and B at the same initial temperature are simultaneously placed in a furnace. The surfaces of the shafts remain at the furnace gas temperature at all times after they are introduced into the furnace. The temperature variation in the axial direction of the shafts can be assumed to be negligible. The data related to shafts A and B is given in the following Table.
| Quantity | Shaft A | Shaft B |
| Diameter (m) | 0.4 | 0.1 |
| Thermal conductivity (W/m-K) | 40 | 20 |
| Volumetric heat capacity (J/m3-K) | 2x106 | 2x107 |
The temperature at the centerline of the shaft A reaches 400°C after two hours. The time required (in hours) for the centerline of the shaft B to attain the temperature of 400°C is ________.
2.5 is the correct answer.
Ques 30 GATE 2016 SET-1
A plastic sleeve of outer radius ro = 1 mm covers a wire (radius r = 0.5 mm) carrying electric current. Thermal conductivity of the plastic is 0.15 W/m-K. The heat transfer coefficient on the outer surface of the sleeve exposed to air is 25 W/m2-K. Due to the addition of the plastic cover, the heat transfer from the wire to the ambient will