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Heat Transfer

26 Questions
GATE→2026→Heat Transfer→Heat Transfer
Q1
MCQ[1 Mark]
A body is placed inside a perfectly black enclosure and is allowed to reach thermal equilibrium. According to the Kirchhoff's identity, which one of the following is equal to the emissivity of the body at a given wavelength?
GATE→2026→Heat Transfer→Heat Transfer
Q2
NAT[2 Marks]
In a double pipe cocurrent heat exchanger, operating at steady state, oil (specific heat capacity =2100 J kg−1 ∘C−1= 2100~\text{J kg}^{-1}~^\circ\text{C}^{-1}) entering at 7 kg s−17~\text{kg s}^{-1} at 100 ∘C100~^\circ\text{C} is used to heat water (specific heat capacity =4200 J kg−1 ∘C−1= 4200~\text{J kg}^{-1}~^\circ\text{C}^{-1}) flowing at 3.5 kg s−13.5~\text{kg s}^{-1} from 20 ∘C20~^\circ\text{C} to 50 ∘C50~^\circ\text{C}. If the overall heat transfer coefficient is 291 W m−2 ∘C−1291~\text{W m}^{-2}~^\circ\text{C}^{-1}, the required heat transfer area (in m2\text{m}^2) is ______ (rounded off to one decimal place).
GATE→2026→Heat Transfer→Heat Transfer
Q3
NAT[2 Marks]
A pipe with outer diameter of 0.02 m, carries hot water. The temperature at the outer surface of the pipe is 70 ∘C70~^\circ\text{C}. This pipe is covered with two concentric layers of insulation, each having a thickness of 0.01 m. The first layer (adjacent to the pipe) is made up of felt material (kf=0.12 W m−1 ∘C−1k_f = 0.12~\text{W m}^{-1}~^\circ\text{C}^{-1}), and the next layer is made up of asbestos (kas=0.15 W m−1 ∘C−1k_{as} = 0.15~\text{W m}^{-1}~^\circ\text{C}^{-1}). The insulated pipe is exposed to ambient air at 20 ∘C20~^\circ\text{C}. The convection heat transfer coefficient at the outer insulation layer is 3 W m−2 ∘C−13~\text{W m}^{-2}~^\circ\text{C}^{-1}. At steady state, neglecting heat transfer due to radiation, the heat loss at the outer insulation layer (in W m−1\text{W m}^{-1}) is ______ (rounded off to two decimal places).
GATE→2025→Heat Transfer→Heat Transfer
Q4
MCQ[1 Mark]
In industrial heat exchanger design, the overall heat transfer coefficient U is estimated from the equation 1U=1hi+1ho\frac{1}{U}=\frac{1}{h_{i}}+\frac{1}{h_{o}}. This is valid for (i) tube of (ii) thermal conductivity.
GATE→2025→Heat Transfer→Heat Transfer
Q5
MSQ[1 Mark]
Which of the following statements regarding multiple effect evaporators is/are TRUE?
GATE→2025→Heat Transfer→Heat Transfer
Q6
MCQ[2 Marks]
A hot plate is placed in contact with a cold plate of a different thermal conductivity as shown in the figure. Which one of the following is an appropriate boundary condition at the surface S?
Figure for Question 6
GATE→2025→Heat Transfer→Heat Transfer
Q7
NAT[2 Marks]
Water flowing at 70 kg/min70\text{ kg/min} is heated from 25∘C25^{\circ}\text{C} to 65∘C65^{\circ}\text{C} in a counter-flow double pipe heat exchanger using hot oil... the heat exchanger area is ______ m2\text{m}^2 (rounded off to 1 decimal place).
GATE→2025→Heat Transfer→Heat Transfer
Q8
NAT[2 Marks]
Consider laminar flow of water over a wide flat plate maintained at uniform temperature... distance xx from leading edge at which thermal boundary layer thickness δT=0.01\delta_T = 0.01 m is ______ m (rounded off to 1 decimal place).
Figure for Question 8
GATE→2025→Heat Transfer→Heat Transfer
Q9
NAT[2 Marks]
An electrical wire... insulated with a plastic layer... steady state temperature at the wire-insulation interface is ______ °C (rounded off to 1 decimal place).
GATE→2024→Heat Transfer→Heat Transfer
Q10
MSQ[1 Mark]
If the Prandtl number Pr=0.01Pr = 0.01, which of the following statements is/are correct?
GATE→2024→Heat Transfer→Heat Transfer
Q11
NAT[1 Mark]
Metal slab of thickness 55 cm, k=400 W m−1 ∘C−1k = 400 \text{ W m}^{-1}~^\circ\text{C}^{-1}, faces at 500∘C500^\circ\text{C} and 200∘C200^\circ\text{C}, area 0.02 m20.02 \text{ m}^2. Heat transfer rate in kW is.
GATE→2024→Heat Transfer→Heat Transfer
Q12
MCQ[2 Marks]
Temperatures of two parallel plates are 900 K and 300 K. A radiation shield is placed between them. Steady-state temperature of the shield is K.
GATE→2024→Heat Transfer→Heat Transfer
Q13
MCQ[2 Marks]
Hot oil at 110∘C110^\circ\text{C} heats water from 30∘C30^\circ\text{C} to 70∘C70^\circ\text{C} in a counter-current double-pipe heat exchanger... heat transfer area in m2\text{m}^2 is
GATE→2024→Heat Transfer→Heat Transfer
Q14
MCQ[2 Marks]
Solid slab of thickness H1H_1... time required for temperature at mid-plane to reach 99% of final value is τ1\tau_1. If thickness is doubled to H2=2H1H_2 = 2 H_1, ratio τ2/τ1\tau_2 / \tau_1 is
GATE→2023→Heat Transfer→Heat Transfer
Q15
MCQ[1 Mark]
Match quantities in Group 1 with units in Group 2
GATE→2023→Heat Transfer→Heat Transfer
Q16
MCQ[1 Mark]
Slab of thickness LL, area AA, conductivity kk. Thermal resistance for steady 1D heat conduction is
Figure for Question 16
GATE→2023→Heat Transfer→Heat Transfer
Q17
MSQ[1 Mark]
Given total hemispherical emissive power EE, which statements are CORRECT?
GATE→2023→Heat Transfer→Heat Transfer
Q18
MSQ[2 Marks]
Which of the following dimensionless numbers include specified terms?
GATE→2023→Heat Transfer→Heat Transfer
Q19
NAT[2 Marks]
Laminar flow over rectangular plate. Value of ratio of average heat transfer coefficients h‾w\overline{h}_w to h‾l\overline{h}_l is.
GATE→2023→Heat Transfer→Heat Transfer
Q20
NAT[2 Marks]
Concentric tube countercurrent heat exchanger cooling oil with water. Number of transfer units (NTU) is.
Figure for Question 20
GATE→2022→Heat Transfer→Heat Transfer
Q21
NAT[1 Mark]
Double pipe heat exchanger with steam condensing at 100∘C100^\circ\text{C} heating water from 75∘C75^\circ\text{C} to 95∘C95^\circ\text{C}. Required cooling water flow rate is kg s−1\text{kg s}^{-1}.
GATE→2022→Heat Transfer→Heat Transfer
Q22
MCQ[2 Marks]
Bare wire coated with insulation. Maximum allowed thermal conductivity to reduce heat loss is W m−1^{-1} K−1^{-1}.
GATE→2022→Heat Transfer→Heat Transfer
Q23
MCQ[2 Marks]
Two planar walls at 1000 K and 500 K with radiation shields melting at 900 K. Maximum number of shields that can be installed is
GATE→2022→Heat Transfer→Heat Transfer
Q24
MCQ[2 Marks]
Saturated steam condensation on vertical plate. Ratio of average heat transfer coefficient over entire plate to that at bottom is
GATE→2022→Heat Transfer→Heat Transfer
Q25
NAT[2 Marks]
Cylindrical fin of diameter 2424 mm with fin effectiveness 1010. Its length is mm.
GATE→2022→Heat Transfer→Heat Transfer
Q26
NAT[2 Marks]
Single-effect evaporator specifications given. Overall heat transfer coefficient is kcal h−1m−2K−1\text{kcal h}^{-1}\text{m}^{-2}\text{K}^{-1}.