GATE Prev Year : Heat-Transfer Test-8

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Question 1

In a case of one dimensional heat conduction in a medium with constant properties, T is the temperature at position x, at time t. thenis proportional to

• A
• B
• C
• D

Question 2

As the temperature increases, the thermal conductivity of a gas

• Aincreases
• Bdecreases
• Cremains constant
• Dincreases up to a certain temperature and then decreases

Question 3

Heat is being transferred by convection from water at 48 °C to a glass plate whose surface that is exposed to the water is at 40 °C. The thermal conductivity of water is 0.6 W/mK and the thermal conductivity of glass is 1.2 W/mK. The spatial gradient of temperature in the water at the water-glass interface is dT/dy = 1×10⁴ K/m.

The value of the temperature gradient in the glass at the water-glass interface is K/m is

• A –2 × 10⁴
• B 0.0
• C 0.5 × 10⁴
• D 2 × 10⁴

Question 4

Heat is being transferred by convection from water at 48 °C to a glass plate whose surface that is exposed to the water is at 40 °C. The thermal conductivity of water is 0.6 W/mK and the thermal conductivity of glass is 1.2 W/mK. The spatial gradient of temperature in the water at the water-glass interface is dT/dy = 1×10⁴ K/m.

The heat transfer coefficient h in W/m² K is

• A 0.0
• B 4.8
• C 6
• D 750

Question 5

The fundamental concept of boundary layer defines boundary layer as layer of fluid developing in flows with very high Reynolds Numbers Re having low viscosity as compared with inertia forces. This is observed when bodies are exposed to high velocity air stream or when bodies are very large and the air stream velocity is moderate.

Computation of boundary layer parameters is obtained from:

• AReynold Number
• BNavier–Stokes equation
• CEulers equation
• DViscous liquids

Question 6

The fundamental concept of boundary layer defines boundary layer as layer of fluid developing in flows with very high Reynolds Numbers Re having low viscosity as compared with inertia forces. This is observed when bodies are exposed to high velocity air stream or when bodies are very large and the air stream velocity is moderate.

The expression for Reynolds Number for the flow in circular pipe is given as:

• ARe_D = uDρ/ή
• BRe_D = u + Dρ/ή
• CRe_D = 1+uDρ/ή
• DRe_D = uDρή

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